View source for Viola (plant)

{{about|the genus of flowering plants||Viola (disambiguation)}}
{{Short description|Genus of flowering plants}}
{{Automatic taxobox
| image = Viola reichenbachiana LC0128.jpg
| image_caption = ''[[Viola reichenbachiana]]''
| display_parents = 2
| taxon = Viola (plant)
| authority = [[Carl Linnaeus|L.]]
| subdivision_ranks = [[Section (botany)|Sections]]
| subdivision = ''see'' [[#Subdivision|Subdivision]]
| type_species = ''[[Viola odorata]]''
| type_species_authority = L.
| synonyms_ref = <ref>{{Cite web |title=Viola L. {{!}} Plants of the World Online {{!}} Kew Science |url=http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30000540-2 |access-date=2023-09-27 |website=Plants of the World Online |language=en}}</ref>
| synonyms = {{hidden begin|title = List}} 
* ''Chrysion'' <small>Spach</small>
* ''Cittaronium'' <small>Rchb.</small>
* ''Crocion'' <small>Nieuwl.</small>
* ''Dischidium'' <small>Rchb.</small>
* ''Erpetion'' <small>DC. ex Sweet</small>
* ''Grammeionium'' <small>Rchb.</small>
* ''Ion'' <small>Medik.</small>
* ''Jacea'' <small>Opiz</small>
* ''Lophion'' <small>Spach</small>
* ''Mnemion'' <small>Spach</small>
* ''Oionychion'' <small>Nieuwl.</small>
{{hidden end}}
}}

'''''Viola''''', commonly known as the '''violets''', is a [[genus]] of [[flowering plant]]s in the family [[Violaceae]]. It is the largest genus in the family, containing over 680 species. Most species are found in the [[temperateness|temperate]] Northern Hemisphere; however, some are also found in widely divergent areas such as [[Hawaii]], [[Australasia]], and the [[Andes]].

Some ''Viola'' species are [[perennial plant]]s, some are [[annual plant]]s, and a few are small [[shrub]]s. Many species, varieties and [[cultivar]]s are grown in gardens for their ornamental flowers. In [[horticulture]], the term [[pansy]] is normally used for those multi-colored large-flowered cultivars which are raised annually or biennially from seed and used extensively in [[bedding (horticulture)|bedding]]. 

== Description ==
[[File:Akkerviooltje opengesprongen doosvrucht.jpg|thumb|Opened seed capsule of ''[[Viola arvensis]]'' (field pansy, ''Melanium''), showing the seeds]]
''Viola'' species can be [[Annual plant|annual]] or [[Perennial plant|perennial]], and can take the form of [[Herbaceous plant|herbs]], [[shrubs]] or very rarely treelets. In acaulescent [[taxa]] the foliage and flowers appear to rise from the ground. The remainder have short stems with foliage and flowers produced in the axils of the leaves (axillary).{{sfn|Ballard et al|2013}}

They typically have heart-shaped or reniform (kidney-shaped) scalloped [[leaf|leaves]], though a number have linear or palmate leaves.{{sfn|Ballard et al|2013}} The simple leaves of plants with either habit are arranged alternately; the acaulescent species produce basal rosettes. Plants always have leaves with [[stipule]]s that are often leaf-like.

The [[flower]]s of the vast majority of the species are strongly [[zygomorphic]] with [[bilateral symmetry]] and solitary, but occasionally form [[cymes]]. The flowers are formed from five [[petals]]; four are upswept or fan-shaped with two per side, and there is one, broad, lobed lower petal pointing downward. This petal may be slightly or much shorter than the others and is weakly differentiated. The shape of the petals and placement defines many species, for example, some species have a "spur" on the end of each petal while most have a spur on the lower petal. The spur may vary from scarcely [[exserted]] (projecting) to very long, such as in ''[[Viola rostrata]]''.{{sfn|Ballard et al|2013}}

Solitary flowers end long stalks with a pair of [[bracteoles]]. The flowers have five [[sepals]] that persist after blooming, and in some species the sepals enlarge after blooming. The [[Corolla (botany)|corolla]] ranges from white to yellow, orange or various shades of blue and [[Violet (color)|violet]] or multicolored, often blue and yellow, with or without a yellow throat.{{sfn|Ballard et al|2013}}

The flowers have five free [[stamens]] with short free filaments that are oppressed against the [[Ovary (botany)|ovary]], with a dorsal connective appendage that is large, entire and oblong to ovate. Only the lower two stamens are [[calcarate]] (possessing [[nectary]] spurs that are inserted on the lowest petal into the spur or a pouch). The [[Style (botany)|styles]] are [[Glossary of botanical terms#Filiform|filiform]] (threadlike) or [[Glossary of botanical terms#clavate|clavate]] (clubshaped), thickened at their tip, being [[globose]] to [[Glossary of botanical terms#rostellate|rostellate]] (beaked). The [[Stigma (botany)|stigmas]] are head-like, narrowed or often beaked. The flowers have a superior ovary with one cell, which has three [[placentae]], containing many ovules.{{sfn|Ballard et al|2013}}

After flowering, [[fruit]] [[capsule (fruit)|capsules]] are produced that are thick walled, with few to many [[seeds]] per [[carpel]], and [[dehisce]] (split open) by way of three valves.{{sfn|Cullen|2001|loc=p.&nbsp;345}} On drying, the capsules may eject seeds with considerable force to distances of several meters.{{sfn|Rendle|1925|loc=p.&nbsp;208}} The nutlike seeds, which are obovoid to globose, are typically [[arillate]] (with a specialized outgrowth) and have straight [[Embryo#plant embryos|embryos]], flat [[cotyledons]], and soft fleshy [[endosperm]] that is oily.{{sfn|Cronquist|1981}}{{sfn|Ballard et al|2013}}

===Phytochemistry===
One characteristic of some ''Viola'' is the elusive scent of their flowers; along with [[terpene]]s, a major component of the scent is a [[ketone]] compound called [[ionone]], which temporarily desensitizes the [[olfactory receptor neuron|receptors]] of the nose, thus preventing any further scent being detected from the flower until the nerves recover.{{sfn|Maxwell|2017}}

==Taxonomy==
[[File:Linnaeus Viola.png|thumb|upright|[[Carl Linnaeus|Linnaeus]]' original description (1753)|alt=First page of Linnaeus' 1753 description of Viola]]

===History===
First formally described by [[Carl Linnaeus]] in 1753{{sfn|Linnaeus|1753}} with 19 species, the genus ''Viola'' bears his [[botanical authority]], L.{{sfn|WFO|2019}} When [[Antoine Laurent de Jussieu|Jussieu]] established the hierarchical system of families (1789), he placed Viola in the [[Cisti]] (rock roses),{{sfn|Jussieu|1789}} though by 1811 he suggested Viola be separated from these.{{sfn|Lindley|1853}} However, in 1802 [[Batsch]] had already established a separate family, which he called Violariae based on Viola as the [[type genus]], with seven other genera.{{sfn|Batsch|1802}}{{sfn|IPNI|2020}} Although Violariae continued to be used by some authors, such as [[Bentham and Hooker]] in 1862 (as Violarieae),{{sfn|Bentham|Hooker|1862}} most authors adopted the alternative name Violaceae, first proposed by [[de Lamarck]] and [[de Candolle]] in 1805,{{sfn|de Lamarck|de Candolle|1815}} and [[Frédéric Charles Jean Gingins de la Sarraz|Gingins]] (1823){{sfn|Gingins|1823}} and [[Augustin Saint-Hilaire|Saint-Hilaire]] (1824).{{sfn|Saint-Hilaire|1824}} However de Candolle also used Violarieae in his 1824 ''Prodromus''.{{sfn|Candolle|1824}}

===Phylogeny===
''Viola'' is one of about 25 genera and about 600 species in the large [[eudicot]] family [[Violaceae]], divided into subfamilies and tribes. While most genera are [[monotypic]], ''Viola'' is a very large genus, variously circumscribed as having between 500 and 600 species. Historically it was placed in subfamily Violoideae, tribe Violeae. But these divisions have been shown to be artificial and not [[monophyletic]]. [[Molecular phylogenetic]] studies show that ''Viola'' occurs in Clade I of the family, as ''Viola'', ''[[Schweiggeria]]'', ''[[Noisettia]]'' and ''[[Allexis]]'', in which ''Schweiggeria'' and ''Noisettia'' are monotypic and form a sister group to ''Viola''.{{sfn|Wahlert et al|2014}}{{sfn|Yockteng et al|2003}}{{sfn|Ballard et al|1998}}

===Subdivision===
''Viola'' is a large genus that has traditionally been treated in [[Sections (botany)|sections]].{{sfn|Yockteng et al|2003}} One of these was that of [[Frédéric Charles Jean Gingins de la Sarraz|Gingins]] (1823),{{sfn|Gingins|1823}} based on stigma morphology, with five sections (''Nomimium'', ''Dischidium'', ''Chamaemelanium'', ''Melanium'', ''Leptidium'').{{sfn|Yoo|Jang|2010}} The extensive taxonomic studies of [[Wilhelm Becker]], culminating in his 1925 conspectus, resulted in 14 sections and many infrasectional groups. The largest and most diverse, being section ''Viola'', with 17 subsections. In addition to subsections, [[Series (biology)|series]] were also described.{{sfn|Becker|1925}} Alternatively, some authors have preferred to subdivide the genus into subgenera. Subsequent treatments were by Gershoy (1934){{sfn|Gershoy|1934}} and Clausen (1964),{{sfn|Clausen|1964}} using subsections and series. These were all based on morphological characteristics. Subsequent studies using [[molecular phylogenetic]] methods, such as that of Ballard et al. (1998) have shown that many of these traditional divisions are not [[monophyletic]], the problem being related to a high degree of [[hybridization (biology)|hybridization]]. In particular section ''Nomimium'' was dismembered into several new sections and transferring part of it to section ''Viola''. Section Viola ''s. lat.'' is represented by four sections, ''Viola'' ''sensu stricto'', ''Plagiostigma'' ''s. str.'', ''Nosphinium'' ''sensu lato''. and the ''V. spathulata'' group. In that analysis, the S American sections appear to be the [[basal group]]s, starting with ''Rubellium'', then ''Leptidium''. However, the exact phylogenetic relationships remain unresolved, as a consequence many different taxonomic nomenclatures are in use, including groupings referred to as [[Grex (horticulture)|Grex]].{{sfn|Ballard et al|1998}} Marcussen et al. place the five S American sections, ''Andinium'', ''Leptidium'', ''Tridens'', ''Rubellium'' and ''Chilenium'' at the base of the phylogenetic tree, in that order. These are followed by the single Australian section, ''Erpetion'', as sister group to ''Chilenium'', the northern hemisphere sections and finally the single African section, ''V. abyssinica''. These sections are morphologically, chromosomally, and geographically distinct.{{sfn|Marcussen et al|2015}}{{sfn|Fan et al|2015}}{{sfn|Malobecki et al|2016}}

====Sections====
Seventeen sections are recognized, listed alphabetically (approximate no. species);{{sfn|Marcussen et al|2012}}{{sfn|Marcussen et al|2015}}{{sfn|Watson et al|2019}}

* Sect. ''Andinium'' <small>W.Becker</small> (113) S America{{sfn|Watson et al|2019}}
* Sect. ''Chamaemelanium'' <small>Ging.</small> ''[[s.lat.]]'' (61) N America, northeast Asia (includes ''Dischidium'', ''Orbiculares'')
** Subsect. ''Chamaemelanium''
** Subsect. ''Nudicaules''
** Subsect. ''Nuttalianae''
* Sect. ''Chilenium'' <small>W.Becker</small> (8) southern S America{{sfn|BioLib|2019}}
* Sect. ''Danxiaviola'' <small>W. B. Liao et Q. Fan</small> (1) China{{sfn|Fan et al|2015}}
* Sect. ''Delphiniopsis'' <small>W.Becker</small> (3) western Eurasia: southern Spain; Balkans{{sfn|CSIC|2020}}
* Sect. ''Erpetion'' <small>(Banks) W.Becker</small> (11–18) eastern Australia; Tasmania 
* Sect. ''Leptidium'' <small>Ging.</small> (19) S America{{sfn|Freitas|Sosa|2002}}
* Sect. ''Melanium'' <small>Ging.</small> (125) western Eurasia (pansies){{sfn|Yockteng et al|2003}}{{sfn|Magrini|Scoppola|2015}}
* Sect. ''Nosphinium'' <small>W.Becker</small> ''s.lat.'' (31–50) N, C and northern S America; Beringia; Hawaii{{sfn|Marcussen et al|2012}} 
* Sect. nov. A (''V. abyssinica'' group) (1–3) Africa: equatorial high mountains 
* Sect. nov. B (''V. spathulata'' group) (7–9) western and central Asia: northern Iraq to Mongolia{{sfn|Fan et al|2015}} 
* Sect. ''Plagiostigma'' <small>Godr.</small> (120) northern hemisphere (includes ''Diffusae''){{sfn|Ning|2012}}{{sfn|Zhou|2008}}{{sfn|Tikhomirov |2015}}
** Grex Primulifolia
* Sect. ''Rubellium'' <small>W.Becker</small> (3–6) S America: Chile{{sfn|Ballard et al|1998}}
* Sect. ''Sclerosium'' <small>W.Becker</small> (1–4) northeastern Africa to southwestern Asia{{sfn|Shahrestani et al|2014}}
* Sect. ''Tridens'' <small>W.Becker</small> (2) southern S America 
* Sect. ''Viola''  ''s.str.'' (''Rostellatae'' ''[[nom. illeg.]]'') (75) northern hemisphere (violets) (includes ''Repentes''){{sfn|Malobecki et al|2016}}
** Subsect. ''Rostratae'' <small>Kupffer (W.Becker)</small>{{sfn|Danihelka|2010}}
** Subsect. ''Viola''
* Sect. ''Xylinosium'' <small>W.Becker</small> (3–4) Mediterranean region

====Species====
The genus includes [[dog violet]]s, a group of scentless species which are the most common ''Viola'' in many areas, sweet violet (''[[Viola odorata]]'') (named from its sweet scent), and many other species whose common name includes the word "violet". But not other "violets": Neither [[Streptocarpus sect. Saintpaulia|''Streptocarpus'' sect. ''Saintpaulia'']] ("African violets", [[Gesneriaceae]]) nor ''[[Erythronium dens-canis]]'' ("dogtooth violets", [[Liliaceae]]) are related to ''Viola''.

=====List of selected species=====
{{Main list|List of Viola species}}
{|
|[[File:Viola canina 100.jpg|upright|thumb|130px|''[[Viola canina]]''|alt=Viola canina flower and leaves]]

======Section ''Andinium''======
With about 113 species, the South American section ''Andinium'' is the largest of the ''Viola'' sections. It is one of the four sections distributed primarily or exclusively in South America, and the basal group of Viola. New species continue to be identified.{{sfn|Gonzáles |Cano|2016}} Species include;{{sfn|Ballard|Iltis|2012}}
* ''[[Viola escarapela]]''{{sfn|Watson|Flores|2003}} 
* ''[[Viola lilliputana]]''{{sfn|Ballard|Iltis|2012}} 
{{clear}}
[[File:Viola biflora Kilpisjarvi 2012-07.jpg|upright|thumb|130px|''[[Viola biflora]]''|alt=Viola biflora flower and leaves]]

======Section ''Chamaemelanium''======
''Chamaemelanium'' was one of a number of sections originally classified on the basis of the shape of the stigma, in this case one that was facial shaped, had an absent beak and had lateral beards. But this section has subsequently been shown to be paraphyletic, requiring revision. It occurs at high altitudes (above 600&nbsp;m) in both N America and northeast Asia, including Siberia and Korea, and the species are perennial, caulous and herbaceous.{{sfn|Whang|2002}} With about 61 species including;
* ''[[Viola biflora]]'' – yellow wood violet, twoflower violet
* ''[[Viola glabella]]'' – stream violet
* ''[[Viola pedunculata]]'' – yellow pansy 
* ''[[Viola praemorsa]]'' – canary violet 
* ''[[Viola pubescens]]'' – downy yellow violet 
|} 
{{clear}}
{|
|[[File:Viola reichei.JPG|upright|thumb|130px|''[[Viola reichei]]''|alt=Viola reichei]]

======Section ''Chilenium''======
A small S American section with about 8 species, as sister group to ''Erpetion'', including;
* ''[[Viola reichei]]''
|} 
{{clear}}
Section ''Danxiaviola''
* ''[[Viola hybanthoides]]''

Section ''Delphiniopsis''
[[File:JDCANO Viola Cazorlensis.jpg|thumb|upright|''Viola Cazorlensis''|alt=Viola Cazorlensis]]
* ''[[Viola cazorlensis]]''
* ''[[Viola delphinantha]]''
* ''[[Viola kosaninii]]''

Section ''Erpetion''{{sfn|Thiele|Prober|2003}}
[[File:Viola banksii.jpg|thumb|upright|''Viola banksii''|alt=Viola banksii]]
* ''[[Viola banksii]]'' – Australian native violet, ivy-leaved violet
* ''[[Viola hederacea]]'' – Australian native violet, ivy-leaved violet

Section ''Leptidium''
[[File:Viola stipularis-La Soufrière-Guadeloupe 1.JPG|thumb|upright|''[[Viola stipularis]]''|alt=Viola stipularis]]
* ''[[Viola stipularis]]''

Section ''Melanium'' (pansies){{sfn|Yockteng et al|2003}}{{sfn|Chervin et al|2019}}
[[File:Common Violet.JPG|thumb|upright|''[[Viola tricolor]]''|alt=Flowers of Viola tricolor]]
* ''[[Viola arvensis]]'' – field pansy
* ''[[Viola bicolor]]''
* ''[[Viola pedunculata]]'' – yellow pansy, [[Pacific Ocean|Pacific]] coast.
* ''[[Viola bertolonii]]''
* ''[[Viola calcarata]]''
* ''[[Viola cheiranthifolia]]'' – Teide violet
* ''[[Viola cornuta]]''
* ''[[Viola lutea]]''
* ''[[Viola tricolor]]'' – wild pansy, heartsease

Section ''Nosphinium''
[[File:Viola pedata.jpg|thumb|upright|''[[Viola pedata]]''|alt=Flowers of Viola pedata]]
* ''[[Viola pedata]]''

Section A (''V. abyssinica'' group)
[[File:Viola abyssinica mt kenya 01.jpg|thumb|upright|''[[Viola abyssinica]]''|alt=Flower of Viola abyssinica]]
* ''[[Viola abyssinica]]''

Section B (''V. spathulata'' group)
* ''[[Viola spathulata]]''

Section ''Plagiostigma''
[[File:Viola epipsila 5999.jpg|thumb|upright|''[[Viola epipsila]]''|alt=Flower of Viola epipsila]]
* ''[[Viola epipsila]]''

Section ''Rubellium''
* ''[[Viola capillaris]]''{{sfn|V capillaris|2020}}
* ''[[Viola portalesia]]''{{sfn|Watson|Watson|2012}}
* ''[[Viola rubella]]''

Section ''Sclerosium'' 
* ''[[Viola cinerea]]''

Section ''Tridens''
[[File:Three-Toothed Violet (3279657452).jpg|thumb|upright|''[[Viola tridentata]]''|alt=Flowers of Viola tridentata]]
* ''[[Viola tridentata]]'' – mountain violet

Section ''Viola'' (violets)
[[File:Trip And Spring 005.jpg|thumb|upright| ''[[Viola sororia]]''|alt=Flowers of Viola sororia]]
* ''[[Viola canina]]'' – heath dog violet
* ''[[Viola hirta]]'' – hairy violet 
* ''[[Viola labradorica]]'' – alpine violet
* ''[[Viola odorata]]'' – sweet violet
* ''[[Viola persicifolia]]'' – fen violet
* ''[[Viola riviniana]]'' – common dog violet
* ''[[Viola rostrata]]'' – long-spurred violet
* ''[[Viola sororia]]'' – common blue violet, hooded violet

Section ''Xylinosium''
[[File:Viola decumbens Kogelberg.jpg|thumb|upright| ''[[Viola decumbens]]''|alt=Flower of Viola decumbens]]
* ''[[Viola decumbens]]''

===Evolution and biogeography===
One [[fossil]] seed of †'''''Viola rimosa''''' has been extracted from [[borehole]] samples of the [[Middle Miocene]] fresh water deposits in [[Nowy Sacz]] Basin, [[West Carpathians]], [[Poland]].{{sfn|Łańcucka-Środoniowa|1979}} The genus is thought to have arisen in S America, most likely the Andes.{{sfn|Yockteng et al|2003}}{{sfn|Ballard et al|1998}}

===Genetics===
[[Habitat fragmentation]] has been shown to have minimal effect on the genetic diversity and gene flow of the North American woodland violet ''Viola pubescens.''{{sfn|Culley et al|2007}} This may be partially attributed to the ability of ''Viola pubescens'' to continue to persist within a largely agricultural matrix.{{sfn|Culley|Grubb|2003}} This trend of unexpectedly high genetic diversity is also observed in ''Viola palmensis'', a Canary Island endemic known only from a 15 square kilometer range on La palma island.{{sfn|Batista|Sosa|2002}} High levels of genetic diversity within these species indicate that these plants are outcrossing, even though many violet species can produce many clonal offspring throughout the year via cleistogamous flowers. Plants that produce copious amounts of clonal seeds from cleistogamous flowers often experience increased levels of inbreeding.{{sfn|Culley|Klooster|2007}} These reportedly high rates of outcrossing and genetic diversity indicate that these violets are strong competitors for pollinators during the early spring when they are in bloom and that those pollinators can travel considerable distances between often fragmented populations.

==Distribution and habitat==
The worldwide northern temperate distribution of the genus distinguishes it from the remaining largely tropical Violaceae genera, restricted to either Old World or New World species, while in the tropics the distribution is primarily in high mountainous areas.{{sfn|Ballard et al|2013}} [[Centres of diversity]] occur mainly in the northern hemisphere, in mountainous regions of eastern Asia, Melanesia, and southern Europe, but also occur in the Andes and the southern Patagonian cone of South America.{{sfn|Ballard|Iltis|2012}} One of the highest species concentrations is in the former USSR.{{sfn|Yoo|Jang|2010}} Australia is home to a number of ''Viola'' species, including ''[[Viola hederacea]]'', ''[[Viola betonicifolia]]'' and ''[[Viola banksii]]'', first collected by [[Joseph Banks]] and [[Daniel Solander]] on the [[James Cook|Cook]] voyage to [[Botany Bay]].{{sfn|Yockteng et al|2003}}

==Ecology==
''Viola'' species are used as food plants by the [[larva]]e of some [[Lepidoptera]] species, including the [[giant leopard moth]], [[large yellow underwing]], [[lesser broad-bordered yellow underwing]], [[high brown fritillary]], [[small pearl-bordered fritillary]], [[pearl-bordered fritillary]], [[regal fritillary]], [[Argynnis pandora|cardinal]], and [[Setaceous Hebrew character]]. The larvae of many fritillary butterfly species use violets as an obligate host plant, although these butterflies do not always oviposit directly onto violets.{{sfn|Kopper et al|2000}} While the ecology of this genera is extremely diverse, violets are mainly pollinated by members within the orders [[Fly|Diptera]] and [[Hymenoptera]].{{sfn|Beattie|1971}} Showy flowers are produced in early spring, and clonal [[Cleistogamy|cleistogamous]] flowers are produced from late spring until the end of the growing season under favorable conditions. Cleistogamy allows plants to produce offspring year round and have more chances for establishment.{{sfn|Lord|1981}} This system is especially important in violets, as these plants are often weak competitors for pollination due to their small size.

Many violet species exhibit two modes of seed dispersal. Once seed capsules have matured, seeds are dispelled around the plant through explosive dehiscence.{{sfn|Beattie|Lyons|1975}} ''Viola pedata'' seeds have been reported being dispersed distances of up to 5 meters away from the parent plant.{{sfn|Beattie|Lyons|1975}} Often, seeds are then further dispersed by ants through a process called [[myrmecochory]].{{sfn|Culver|Beattie|1978}} Violets whose seeds are dispersed this way have specialized structures on the exterior of the seeds called [[elaiosome]]s. This interaction allows violet seed to germinate and establish in a protected, stable environment.{{sfn|Beattie|Lyons|1975}}

Many violet seeds exhibit physiological [[Seed dormancy|dormancy]] and require some period of cold [[Stratification (seeds)|stratification]] to induce germination under ''ex situ'' conditions.{{sfn|Baskin|Baskin|1972}} Rates of germination are often quite poor, especially when seeds are stored for extended periods of time.{{sfn|Elisafenko|2015}} In North American [[Restoration ecology|habitat restoration]], native violets are in high demand due to their relationship with the aforementioned fritillary butterflies.{{sfn|Shuey et al|2016}}

Violet species occupy a diverse array of habitats, from bogs (''[[Viola lanceolata]]'') to dry hill prairies (''[[Viola pedata|V. pedata]]'') to woodland understories (''[[Viola labradorica|V. labradorica]]''). While many of these species are indicators of high quality habitat, some violets are capable of thriving in a human altered landscape. Two species of zinc violet (''[[Viola calaminaria|V. calaminaria]]'' and ''[[Viola guestphalica|V. guestphalica]]'') are capable of living in soils severely contaminated with heavy metals.{{sfn|Hildebrandt et al|1999}} Many violets form relationships with [[Arbuscular mycorrhiza|arbuscular mycorrhizal fungi]], and in the case of the zinc violets, this allows them to tolerate such highly contaminated soils.

Flowering is often profuse, and may last for much of the spring and summer. ''Viola'' are most often spring-blooming with [[chasmogamous]] flowers that have well-developed petals pollinated by insects. Many species also produce self-pollinated [[cleistogamous]] flowers in summer and autumn that do not open and lack petals.{{sfn|Walters|Keil|1996|loc=p.&nbsp;332}} In some species the showy chasmogamous flowers are infertile (e.g.,''[[Viola sororia]]'').{{efn|''V. papilionacea'' is considered a [[synonym (taxonomy)|synonym]] of ''V. sororia''}}{{sfn|VC|2020}}

==Horticultural uses==
The international registration authority for the genus is the [[American Violet Society]], where growers register new Viola [[cultivars]].{{sfn|AVS|2007}} A coding system is used for cultivar description of ten horticultural divisions, such as Violet (Vt) and Violetta (Vtta).{{sfn|RHS|2009}} Examples include ''Viola'' 'Little David' (Vtta){{sfn|RHS Little David|2020}} and ''Viola'' 'Königin Charlotte' (Vt).{{sfn|RHS Konigin Charlotte|2020}}

In this system violets (Vt) are defined as "[[stoloniferous]] perennials with small, highly fragrant, self-coloured purple, blue or white flowers in late winter and early spring".{{sfn|RHS|2009}}

===Species and cultivars===
[[File:Viola x hybrida 'Clear Crystals Apricot', SC, Vic., 15.9.2007.jpg|thumb|upright|''Viola'' cultivar showing the large round flowers and the novel coloration that has been achieved through breeding.]]
Many species, varieties and cultivars are grown in gardens for their ornamental flowers. In horticulture the term '''[[pansy]]''' is normally used for those multi-colored, large-flowered cultivars which are raised annually or biennially from seed and used extensively in [[bedding (horticulture)|bedding]]. The terms '''viola''' and '''violet''' are normally reserved for small-flowered annuals or perennials, including the wild species.{{sfn|AVS|2007}}{{sfn|RHS|2009}}

Cultivars of ''[[Viola cornuta]]'', ''[[Viola cucullata]]'', and ''[[Viola odorata]]'', are commonly grown from seed. Other species often grown include ''[[Viola labradorica]]'', ''[[Viola pedata]]'', and ''[[Viola rotundifolia]]''.{{sfn|Armitage|2008}}

The modern garden [[pansy]] (''V. ''×'' wittrockiana'') is a plant of complex hybrid origin involving at least three species, ''[[Viola tricolor|V. tricolor]]'' (wild pansy or heartsease), ''[[Viola altaica|V. altaica]]'', and ''[[Viola lutea|V. lutea]]'' (mountain pansy).{{sfn|Wittrock|1892–1897a}} The hybrid horned pansy (''[[Viola × williamsii|V.'' × ''williamsii]]'') originates from hybridization involving [[garden pansy]] and ''[[Viola cornuta]]''.{{sfn|Wittrock|1892–1897}}

===Bedding plants===
In 2005 in the United States, ''Viola'' cultivars (including pansies) were one of the top three [[bedding (horticulture)|bedding]] plant crops and 111 million dollars' worth of flats of ''Viola'' were produced for the bedding flower market. Pansies and violas used for bedding are generally raised from seed, and [[F1 hybrid]] seed strains have been developed which produce compact plants of reasonably consistent flower coloring and appearance. Bedding plants are usually discarded after one growing season.{{sfn|Kelly et al|2007}}

===Perennial cultivars===
[[File:Viola cultivars at BBC Gardeners' World - 20110616.jpg|thumb|right|Selection of cultivated violas at the [[Gardeners' World Live]] show, in June 2011.]]
There are hundreds of perennial viola and violetta cultivars; many of these do not breed true from seed and therefore have to be [[Plant propagation|propagated]] from cuttings. Violettas can be distinguished from violas by the lack of ray markings on their petals.{{sfn|AVS|2007}} The following cultivars, of mixed or uncertain parentage, have gained the [[Royal Horticultural Society]]'s [[Award of Garden Merit]]:{{sfn|RHS|2018}}
{{div col|colwidth=15em}}
* 'Aspasia'<ref>{{cite web | title=RHS Plant Selector ''Viola'' 'Aspasia' | url = https://www.rhs.org.uk/Plants/69362/Viola-Aspasia-(Va)/Details | publisher = RHS | access-date = 5 March 2021}}</ref>
* 'Clementina'<ref>{{cite web | title=RHS Plant Selector ''Viola'' 'Clementina' | url = https://www.rhs.org.uk/Plants/86348/Viola-Clementina-(Va)/Details | publisher = RHS | access-date = 5 March 2021}}</ref>
* 'Huntercombe Purple'<ref>{{cite web | title=RHS Plant Selector ''Viola'' 'Huntercombe Purple' | url=https://www.rhs.org.uk/Plants/55414/Viola-Huntercombe-Purple-(Va)/Details | access-date = 5 March 2021}}</ref>
* 'Jackanapes'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/82434/Viola-Jackanapes-(Va)/Details | title = ''Viola'' 'Jackanapes' | publisher = RHS | access-date = 5 March 2021}}</ref>
* 'Molly Sanderson'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/82731/Viola-Molly-Sanderson-(Va)/Details | title = ''Viola'' 'Molly Sanderson' | publisher = RHS | access-date = 5 March 2021}}</ref> 
* 'Moonlight'<ref>{{cite web | title=RHS Plant Selector ''Viola'' 'Moonlight' | url=https://www.rhs.org.uk/Plants/77516/Viola-Moonlight-(Va)/Details | access-date = 5 March 2021}}</ref>
* 'Nellie Britton'<ref>{{cite web | title=RHS Plant Selector ''Viola'' 'Nellie Britton' | url=https://www.rhs.org.uk/Plants/52163/Viola-Nellie-Britton-(Va)/Details|access-date=17 March 2021}}</ref>
{{div col end}}

Other popular examples include:<ref>''RHS Plant Finder 2008-2009'', Dorling Kindersley (2008) {{ISBN|978-1-4053-3190-6}} pp787–791</ref>
{{div col|colwidth=15em}}
*'Ardross Gem' (viola)
*'Blackjack'
*'Buttercup' (violetta)
*'Columbine' (viola)
*'Dawn' (violetta)
*'Etain' (viola)
*'Irish Molly' (viola)
*'Maggie Mott' (viola)
*'Martin' (viola)
*'Rebecca' (violetta)
*'Vita' (viola)
*'Zoe' (violetta)
{{div col end}}

==Other uses==
===Culinary===
{{anchor|Candied violet}}
[[File:Violet candy from Savoie, 2023.jpg|thumb|Violet-flavored candy]]
[[File:La Violette, Brasserie du Mont-Blanc, 2025.jpg|thumb|French violet-flavored beer]]
When newly opened, ''Viola'' flowers may be used to decorate salads or in stuffings for poultry or fish. Soufflés, cream, and similar desserts can be flavoured with essence of ''Viola'' flowers. The young leaves are edible raw or cooked as a mild-tasting [[leaf vegetable]]. The flowers and leaves of the cultivar 'Rebecca', one of the Violetta violets, have a distinct vanilla flavor with hints of wintergreen. The pungent perfume of some varieties of ''V. odorata'' adds inimitable sweetness to desserts, fruit salads, and teas while the mild pea flavor of ''V. tricolor'' combines equally well with sweet or savory foods, like grilled meats and steamed vegetables. The heart-shaped leaves of ''V. odorata'' provide a free source of greens throughout a long growing season,<ref>{{cite web|last=Whittaker|first=Debbie|title=Cooking and Decorating With Violets|url=http://americanvioletsociety.org/Cooking_N_Decorating/ViolaChef_01.htm|work=The Culinary Violet|publisher=The American Violet Society|access-date=2012-02-09|url-status=live|archive-url=https://web.archive.org/web/20120223050014/http://americanvioletsociety.org/Cooking_N_Decorating/ViolaChef_01.htm|archive-date=2012-02-23}}</ref> while the petals are used for fragrant flavoring in milk puddings and ice cream or in salads and as garnishes.{{sfn|Davidson|2014}}{{sfn|Robuchon|1997}}

A [[Candied fruit|candied]] violet or crystallized violet is a flower, usually of ''Viola odorata'', preserved by a coating of egg white and crystallised sugar. Alternatively, hot syrup is poured over the fresh flower (or the flower is immersed in the syrup) and stirred until the sugar recrystallizes and has dried. This method is still used for [[rose]] petals and was applied to [[Orange (fruit)|orange]] flowers in the past (when [[almond]]s or orange peel are treated this way they are called [[praline (nut confection)|praline]]s). Candied violets are still made commercially in [[Toulouse]], France, where they are known as ''violettes de Toulouse''. They are used as decorating cakes or trifles or included in aromatic desserts.{{sfn|Davidson|2014}}{{sfn|Robuchon|1997}}

The French are also known for their violet [[syrup]], most commonly made from an extract of violets. In the United States, this French violet syrup is used to make violet [[scone]]s and [[marshmallow]]s. ''Viola'' essence flavours the [[liqueurs]] [[Creme Yvette]], [[Creme de Violette]], and [[Parfait d'Amour]]. It is also used in confectionery, such as [[Parma Violets]] and [[C. Howard's Violet candies]].

===Phytochemicals===
Many ''Viola'' species contain [[anthocyanin]]s, such as those from ''V. yedoensis'' and ''V. prionantha''.<ref>{{cite journal | last1=Zhang | first1=J. |display-authors=etal | year=2011 | title=Rapid separation and identification of anthocyanins from flowers of ''Viola yedoensis'' and ''V. prionantha'' by high-performance liquid chromatography-photodiode array detection-electrospray ionisation mass spectrometry | journal=Phytochemical Analysis | volume=23 | issue=1| pages=16–22 | pmid=21523841 | doi=10.1002/pca.1320}}</ref> Most violas tested and many other plants of the family Violaceae contain [[cyclotides]].<ref>{{cite journal | last1=Tang | first1=J. |display-authors=etal | year=2010 | title=''Isolation and characterization of cytotoxic cyclotides from ''Viola tricolor | url=http://210.72.88.198:8080/bitstream/151853/4868/1/201202130060.pdf | journal=Peptides | volume=31 | issue=8 | pages=1434–40 | doi=10.1016/j.peptides.2010.05.004 | pmid=20580652 | s2cid=33157266 | url-status=dead | archive-url=https://web.archive.org/web/20130718062837/http://210.72.88.198:8080/bitstream/151853/4868/1/201202130060.pdf | archive-date=2013-07-18 | access-date=2013-07-03 }}</ref><ref>{{cite journal | last1=Trabi | first1=M. |display-authors=etal | year=2009 | title=Circular proteins from ''Melicytus'' (Violaceae) refine the conserved protein and gene architecture of cyclotides | journal=Organic and Biomolecular Chemistry | volume=7 | issue=11| pages=2378–88 | pmid=19462049 | doi=10.1039/b823020j}}</ref><ref>{{cite journal | last1=Gerlach | first1=S. L. |display-authors=etal | year=2010 | title=''Isolation, characterization, and bioactivity of cyclotides from the Micronesian plant ''Psychotria leptothyrsa | journal=[[Journal of Natural Products]] | volume=73 | issue=7| pages=1207–13 | pmid=20575512 | doi=10.1021/np9007365}}</ref><ref>{{cite journal | last1=Craik | first1=David J. | year=2010 | title=Discovery and applications of the plant cyclotides | journal=Toxicon | volume=56 | issue=7| pages=1092–1102 | doi=10.1016/j.toxicon.2010.02.021 | pmid=20219513 }}</ref>

===Perfume===
''[[Viola odorata]]'' is used as a source for scents in the perfume industry. Violet is known to have a 'flirty' scent as its fragrance comes and goes. [[Ionone]] is present in the flowers, which turns off the ability for humans to smell the fragrant compound for moments at a time.<ref>Ackerman, Diane. A natural history of the senses. New York: Vintage Books, 1991. Print.</ref>

==Cultural associations==

===Birth===
Violet is the traditional [[birth flower]] for February in English tradition.<ref>{{cite web|url=http://www.almanac.com/content/birth-month-flowers-and-their-meanings/|title=Birth Month Flowers and Their Meanings|first=Old Farmer's|last=Almanac}}</ref>

===Geographical territories===
In the United States, the common blue violet ''[[Viola sororia]]'' is the [[List of U.S. state and territory flowers|state flower]] of [[Illinois]],<ref>{{cite web | url=http://www.state.il.us/kids/learn/symbols/ | title=State Symbols | publisher=State of Illinois}}</ref> [[Rhode Island]],<ref>{{cite web|url=https://statesymbolsusa.org/symbol-official-item/rhode-island/state-flower/violet|title=Rhode Island State Flower - Violet|website=statesymbolsusa.org|date=13 October 2014 }}</ref> [[New Jersey]]<ref>{{cite web|url=https://statesymbolsusa.org/symbol-official-item/new-jersey/state-flower/violet|title=New Jersey State Flower - Violet|website=statesymbolsusa.org|date=27 May 2014 }}</ref> and [[Wisconsin]].<ref>{{cite web|title=Wisconsin State Symbols |publisher=State of Wisconsin |url=http://www.wisconsin.gov/state/core/wisconsin_state_symbols.html |access-date=2011-12-19 |url-status=dead |archive-url=https://web.archive.org/web/20100112222837/http://www.wisconsin.gov/state/core/wisconsin_state_symbols.html |archive-date=2010-01-12 }}</ref><ref>{{cite web|url=https://statesymbolsusa.org/wisconsin/flower/wood-violet|title=Wisconsin State Flower - Wood Violet|website=statesymbolsusa.org|date=25 April 2014 }} [[Rhode Island]] and [[Illinois]].</ref> In [[Canada]], the ''[[Viola cucullata]]'' is the provincial flower of [[New Brunswick]], adopted in 1936.<ref>{{cite web | title=New Brunswick | publisher=Government of Canada | date=2013-08-28 | url=http://www.pch.gc.ca/eng/1363284167066 | access-date=2015-07-18 }}</ref> In the United Kingdom, ''[[Viola riviniana]]'' is the county flower of [[Lincolnshire]].<ref>{{cite web|url=http://www.plantlife.org.uk/uk/discover-wild-plants-nature/plant-fungi-species/dog-violet-common|title=Dog-violet (Common)|website=Plantlife|access-date=2018-09-22|archive-date=2023-03-09|archive-url=https://web.archive.org/web/20230309124642/https://www.plantlife.org.uk/uk/discover-wild-plants-nature/plant-fungi-species/dog-violet-common|url-status=dead}}</ref>

===Lesbian and bisexual culture===
Violets became symbolically associated with romantic love between women.<ref>{{cite book|last1=Myers|first1=JoAnne|title=The A to Z of the Lesbian Liberation Movement: Still the Rage (The A to Z Guide Series, No. 73 )|date=2003|publisher=[[The Scarecrow Press]]|location=Lanham, Maryland|page=242|edition=1st|isbn=978-0-8108-6811-3}}</ref><ref>{{cite book|title=The Alyson Almanac: A Treasury of Information for the Gay and Lesbian Community|date=1989|publisher=[[Alyson Publications]]|location=Boston, Massachusetts|page=[https://archive.org/details/alysonalmanactr00bost/page/100 100]|chapter=Gay Symbols Through the Ages|isbn=978-0-932870-19-3|chapter-url=https://archive.org/details/alysonalmanactr00bost|url=https://archive.org/details/alysonalmanactr00bost/page/100}}</ref> This connection originates from fragments of a poem by [[Sappho]] about a lost love, in which she describes her as "Close by my side you put around yourself [many wreaths] of violets and roses."<ref>{{cite book|last1=Collecott|first1=Diana|title=H.D. and Sapphic Modernism 1910-1950|date=1999|publisher=[[Cambridge University Press]]|location=Cambridge, UK|page=216|edition=1st|isbn=978-0-521-55078-9}}</ref> In another poem, Sappho describes her lost love as wearing "violet tiaras, braided rosebuds, dill and crocus twined around" her neck.<ref>{{cite book|last1=Barnard|first1=Mary|title=Sappho: A New Translation|url=https://archive.org/details/sappho00sapp|url-access=registration|date=1958|publisher=[[University of California Press]]|page=42|isbn=9780520223127|edition=1st|lccn=58006520}}</ref> In 1926, one of the first plays to involve a [[lesbian]] relationship, ''[[The Captive (play)|La Prisonnière]]'' by [[Édouard Bourdet]], used a bouquet of violets to signify lesbian love.<ref>{{cite web|last1=Cohen-Stratyner|first1=Barbara|title=Violets and Vandamm|url=https://www.nypl.org/blog/2014/01/14/violets-vandamm|website=[[New York Public Library]]|date=January 14, 2014|access-date=4 October 2018}}</ref><ref>{{cite book|last1=Sova|first1=Dawn B.|title=Banned Plays: Censorship Histories of 125 Stage Dramas|url=https://archive.org/details/bannedplayscenso0000sova|url-access=registration|date=2004|publisher=[[Facts On File]]|pages=[https://archive.org/details/bannedplayscenso0000sova/page/37 37–40]|edition=1st|isbn=978-0-8160-4018-6}}</ref>

===Tributes===

Violets, and badges depicting them,<ref>[http://www.nma.gov.au/collections-search/display?irn=34929 NMA Collections Search] {{webarchive|url=https://web.archive.org/web/20140531105254/http://www.nma.gov.au/collections-search/display?irn=34929 |date=2014-05-31 }} National Museum of Australia (2003-2010) - Violet Day 1917 fundraising badge</ref><ref name="Gracie2012">{{Citation | last=Gracie | first=Carol | year=2012 | title=Spring Wildflowers of the Northeast: A Natural History | pages=221 | isbn=978-0691144665 | publisher=Princeton University Press | location=Princeton, NJ }}</ref>
were sold in fund-raising efforts in Australia and New Zealand on and around [[Violet Day]]<ref>[http://www.ach.familyhistorysa.info/ww1violetday.html Family History South Australia] {{webarchive|url=https://web.archive.org/web/20131109212657/http://www.ach.familyhistorysa.info/ww1violetday.html |date=2013-11-09 }} Leadbeater, B (2006). World War 1 Violet Day South Australia.</ref> in commemoration of the lost soldiers of [[World War I]].<ref>{{cite web|title=Violet Day, Press, 3 September 1914, p.8, col. 8|url=http://paperspast.natlib.govt.nz/cgi-bin/paperspast?a=d&d=CHP19140903.1.8&e=-------10--1----0--|publisher=The National Library of New Zealand|access-date=10 November 2015|page=8|format=Newspaper|date=3 September 1914|url-status=live|archive-url=https://web.archive.org/web/20160305135809/http://paperspast.natlib.govt.nz/cgi-bin/paperspast?a=d|archive-date=5 March 2016}}</ref>

==See also==
* [[Rosalia (festival)]], a festival of roses which sometimes involved violas
* [[Pansy]]

==Notes==
{{Notelist}}

==References==
{{Reflist}}

==Bibliography==
{{Refbegin|30em}}
===Books===
* {{cite book|last=Armitage|first=Allan M.|title=Herbaceous Perennial Plants: A Treatise on their Identification, Culture, and Garden Attributes|edition=3rd|url=https://books.google.com/books?id=kA6VgfxsstIC|date=1 May 2008|orig-year=1989|publisher=[[Cool Springs Press]]|isbn=978-1-61058-380-0|chapter=Viola|pages=1038ff}}{{link note|note=[https://books.google.com/books?id=zQXHjuqht40C additional excerpts]}} 
* {{cite book|last1=Ballard|first1=Harvey E|last2=Paula-Souza|first2=Juliana de|last3=Wahlert|first3=Gregory A|editor-last=Kubitzki|editor-first=Klaus|editor-link=Klaus Kubitzki|title=Flowering Plants. 11 Eudicots: Malpighiales|url=https://books.google.com/books?id=4vlkyAEACAAJ|date=2013|publisher=[[Springer Science & Business Media]]|isbn=978-3-642-39417-1|chapter=Violaceae|pages=303–322|chapter-url=https://www.researchgate.net/publication/270759276|ref={{harvid|Ballard et al|2013}}}}{{link note|note=Also preview at [https://www.springer.com/life+sciences/plant+sciences/book/978-3-642-39416-4 Springer]}}
* {{cite book<!--Deny Citation bot-->|last=Becker|first=Wilhelm|author-link=Wilhelm Becker|title=Die natürlichen Pflanzenfamilien nebst ihren Gattungen und wichtigeren Arten, insbesondere den Nutzpflanzen, unter Mitwirkung zahlreicher hervorragender Fachgelehrten|date=1925|orig-year=1887–1915|language=de|volume=21|publisher=Duncker & Humblot |location=Berlin|url=https://www.duncker-humblot.de/buch/die-natuerlichen-pflanzenfamilien-nebst-ihren-gattungen-und-wichtigeren-arten-insbesondere-den-nutzpflanzen-9783428011513/?page_id=0&typ=buc|editor1-last=Engler|editor1-first=Adolf|editor2-last=Prantl|editor2-first=Karl|editor-link1=Adolf Engler|editor-link2=Karl Anton Prantl|edition=2nd|chapter=Viola|pages=363–376}}
* {{cite book | last=Cronquist | first=Arthur | author-link=Arthur Cronquist | date=1981 | title=An integrated system of classification of flowering plants | url=https://archive.org/details/integratedsystem0000cron | url-access=registration | location=New York | publisher=[[Columbia University Press]] | page=[https://archive.org/details/integratedsystem0000cron/page/404 404] | isbn=9780231038805 }}
* {{cite book|editor-last=Cullen|editor-first=James|title=Handbook of North European Garden Plants: With Keys to Families and Genera|url=https://books.google.com/books?id=N2kxDjY_JgwC|date=2001|publisher=[[Cambridge University Press]]|isbn=978-0-521-00411-4}}
* {{cite book|editor-last1=Cullen|editor-first1=James|editor-last2=Knees|editor-first2=Sabina G.|editor-last3=Cubey|editor-first3=H. Suzanne|last=Walters|first=S M|author-link=S M Walters|title=The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass. Vol IV Aquifoliaceae - Hydropyhllacea|url=https://books.google.com/books?id=yaD8XmgCYHsC|date=2011|orig-year=1984|publisher=[[Cambridge University Press]]|edition=2nd|isbn=978-0-521-76160-4|chapter=Viola Linnaeus|pages=102–107}}
* {{cite book|last=Davidson|first=Alan|title=The Oxford Companion to Food|url=https://books.google.com/books?id=RL6LAwAAQBAJ|year=2014|publisher=[[Oxford University Press]]|chapter=Violet|isbn=978-0-19-967733-7}}, ''see also'' [[The Oxford Companion to Food]]
* {{cite book |last1=Gershoy |first1=A |title=Studies in North American violets. III. Chromosome numbers and species characters. Bulletin no. 367 |date=1934 |publisher=Vermont Agricultural Experiment Station}}
* {{cite book|last=Maxwell|first=Catherine|title=Scents and Sensibility: Perfume in Victorian Literary Culture|chapter-url=https://books.google.com/books?id=cZ83DwAAQBAJ&pg=PA76|date=2017|chapter=Perfumed melodies, Violet memories: Scent and remembrance in the nineteenth century|publisher=[[OUP Oxford]]|isbn=978-0-19-100521-3|pages=66–84}}{{Link note|note=additional excerpts as [https://books.google.com/books?id=7Zg6DwAAQBAJ e-book]}}
* {{cite book|editor-last=Robuchon|editor-first=Joël|title=Larousse gastronomique|url=https://books.google.com/books?id=Pa6SnAEACAAJ|year=1997|publisher=[[Éditions Larousse|Larousse]]|isbn=978-2-03-560227-5|chapter=Violette|page=1106|chapter-url=https://archive.org/details/DictionnaireLarousseGastronomique/page/n1105/mode/2up}}, {{link note|note=''see also'' [[Larousse Gastronomique]]}}
* {{cite book|last=Rendle|first=Alfred Barton|title=The Classification of Flowering Plants: Volume 2, Dicotyledons|url=https://books.google.com/books?id=Fuo8AAAAIAAJ|date=1925|publisher=[[CUP Archive]]|isbn=978-0-521-06057-8}}{{link note|note=Full text [https://www.biodiversitylibrary.org/bibliography/95518#/summary available] at [[Biodiversity Heritage Library|BHL]]}}
* {{cite book|last1=Walters|first1=Dirk R.|last2=Keil|first2=David J.|title=Vascular Plant Taxonomy|url=https://archive.org/details/vascularplanttax00walt|url-access=registration|year=1996|publisher=Kendall/Hunt Publishing Company|edition=4th|isbn=978-0-7872-2108-9}}, {{link note|note=also [https://books.google.com/books?id=ZbaNxSnNoecC available] at [[Google Books]]}}

;Historical sources
* {{cite book|last1=Batsch|first1=August Johann Georg Karl|author-link=August Batsch|title=Tabula affinitatum regni vegetabilis, quam delineavit, et nunc ulterius adumbratam|date=1802|publisher=Landes-Industrie-Comptoir|location=[[Weimar]]|url=https://www.biodiversitylibrary.org/bibliography/7569#/summary|language=la|chapter=Violariae|pages=57–59|chapter-url=https://www.biodiversitylibrary.org/item/31965#page/77/mode/1up}}
* {{cite book|last1=Bentham|first1=G.|last2=Hooker|first2=J.D.|author-link1=George Bentham|author-link2=Joseph Dalton Hooker|title=Genera plantarum ad exemplaria imprimis in herbariis kewensibus servata definita|format=3 vols.|year=1862|publisher=L Reeve & Co.|location=London|url=https://www.biodiversitylibrary.org/bibliography/747#/summary|volume=1|chapter=Violarieae|issue=1|pages=114–121|chapter-url=https://www.biodiversitylibrary.org/item/14680#page/125/mode/1up}}
* {{cite book|last1=de Candolle|first1=A. P.|author-link=Augustin Pyramus de Candolle|title=Prodromus systematis naturalis regni vegetabilis, sive, Enumeratio contracta ordinum generum specierumque plantarum huc usque cognitarium, juxta methodi naturalis, normas digesta 17 vols.|date=1824–1873|publisher=Treuttel et Würtz|location=Paris|url=https://www.biodiversitylibrary.org/bibliography/286#/summary|volume=1|chapter=Violarieae|pages=287–316|chapter-url=https://www.biodiversitylibrary.org/page/154246#page/294/mode/1up|ref={{harvid|Candolle|1824}}}}
* {{cite book |last=Jussieu |first=Antoine Laurent de |author-link=Antoine Laurent de Jussieu |title=Genera plantarum: secundum ordines naturales disposita, juxta methodum in Horto regio parisiensi exaratam, anno M.DCC.LXXIV |location=Paris |year=1789 |oclc=5161409 |url=https://www.biodiversitylibrary.org/item/7125 |language=la |chapter=Cisti: Viola |page=294 |chapter-url=https://www.biodiversitylibrary.org/item/7125#page/389/mode/1up }}
* {{cite book|last1=de Lamarck|first1=Jean-Baptiste|last2=de Candolle|first2=AP|author-link1=Lamarck|author-link2=AP de Candolle|title=Flore française ou descriptions succinctes de toutes les plantes qui croissent naturellement en France disposées selon une nouvelle méthode d'analyse; et précédées par un exposé des principes élémentaires de la botanique|date=1815|orig-year=1805|publisher=Desray|location=Paris|edition=3rd|volume=IV(2)|url=https://books.google.com/books?id=wfATAAAAQAAJ|language=fr|chapter=Violaceae|pages=801−810}} {{link note|note=''Latin Index page 931''}}
* {{cite book|last=Lindley|first=John|author-link=John Lindley|title=The Vegetable Kingdom: or, The structure, classification, and uses of plants, illustrated upon the natural system|publisher=Bradbury & Evans|location=London|date=1853|orig-year=1846|edition=3rd.|url=https://www.biodiversitylibrary.org/bibliography/95459#/summary|chapter=Violaceae|pages=338−339|chapter-url=https://www.biodiversitylibrary.org/item/173373#page/454/mode/1up}}
* {{cite book|last=Linnaeus|first=Carl|author-link=Carl Linnaeus|title=Species Plantarum: exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas|url=https://www.biodiversitylibrary.org/bibliography/669#/summary|year=1753|volume=2|chapter=Viola|chapter-url=https://www.biodiversitylibrary.org/item/13830#page/375/mode/1up|pages=933–937|publisher=Impensis Laurentii Salvii|location=Stockholm}}, ''see also'' [[Species Plantarum]]

===Articles===
* {{cite journal |last1=Baskin |first1=Jerry M. |last2=Baskin |first2=Carol C. |title=Physiological Ecology of Germination of Viola rafinesquii |journal=[[American Journal of Botany]] |date=November 1972 |volume=59 |issue=10 |pages=981–988|doi=10.2307/2441480|jstor=2441480}}
* {{cite journal |last1=Batista |first1=Francisco |last2=Sosa| first2=Pedro A.|title=Allozyme Diversity in Natural Populations of Viola palmensis Webb & Berth. (Violaceae) from La Palma (Canary Islands): Implications for Conservation Genetics |journal=[[Annals of Botany]] |date=31 October 2002 |volume=90 |issue=6 |pages=725–733 |doi=10.1093/aob/mcf256|pmid=12451028|pmc=4240367}}
* {{Cite journal|last=Beattie|first=A. J.|title=Pollination Mechanisms in Viola|date=March 1971|journal=[[New Phytologist]]|volume=70|issue=2|pages=343–360|doi=10.1111/j.1469-8137.1971.tb02533.x|doi-access=}}
* {{Cite journal|last1=Beattie|first1=A. J.|last2=Lyons|first2=N.|title=Seed Dispersal in Viola (Violaceae): Adaptations and Strategies|date=August 1975|journal=[[American Journal of Botany]]|volume=62|issue=7|pages=714–722|doi=10.2307/2442060|jstor=2442060}}
* {{cite journal |last1=Clausen |first1=Jens |title=Cytotaxonomy and distributional ecology of western North American violets |url=https://archive.org/details/madronowest1719631964cali/page/n205/mode/2up |journal=[[Madroño (journal)|Madroño]] |date=1964 |volume=17 |issue=6 |pages=173–197 |jstor=41423141 |issn=0024-9637 }}, ''also at'' [https://www.biodiversitylibrary.org/part/170319#/summary BHL]
* {{cite journal |last1=Culley |first1=Theresa M. |last2=Grubb |first2=Thomas C. |title=Genetic effects of habitat fragmentation in Viola pubescens (Violaceae), a perennial herb with chasmogamous and cleistogamous flowers |journal=Molecular Ecology |date=1 October 2003 |volume=12 |issue=11 |pages=2919–2930 |doi=10.1046/j.1365-294X.2003.01971.x|pmid=14629373 |bibcode=2003MolEc..12.2919C |s2cid=22916831 }}
* {{cite journal |last1=Culley |first1=Theresa M. |last2=Klooster |first2=Matthew R. |title=The Cleistogamous Breeding System: A Review of Its Frequency, Evolution, and Ecology in Angiosperms |url=https://www.researchgate.net/publication/225503104 |journal=[[The Botanical Review]] |date=January 2007 |volume=73 |issue=1 |pages=1–30 |doi=10.1663/0006-8101(2007)73[1:TCBSAR]2.0.CO;2 |s2cid=12223087 }}
* {{cite journal |last1=Culley |first1=T. M. |last2=Sbita |first2=S. J. |last3=Wick |first3=A. |title=Population Genetic Effects of Urban Habitat Fragmentation in the Perennial Herb Viola pubescens (Violaceae) using ISSR Markers |journal=[[Annals of Botany]] |date=13 March 2007 |volume=100 |issue=1 |pages=91–100 |doi=10.1093/aob/mcm077|pmid=17556381|pmc=2735295|ref={{harvid|Culley et al|2007}}}}
* {{cite journal |last1=Culver |first1=David C. |last2=Beattie |first2=Andrew J. |title=Myrmecochory in Viola: Dynamics of Seed-Ant Interactions in Some West Virginia Species |journal=[[The Journal of Ecology]] |date=March 1978 |volume=66 |issue=1 |pages=53–72 |doi=10.2307/2259181|jstor=2259181|bibcode=1978JEcol..66...53C }}
* {{cite journal |last1=Elisafenko |first1=T. V. |title=Features of seed germination in different ecological groups of the species of the section Violidum, subgenus Nomimium, genus Viola L. (Violaceae) |journal=Contemporary Problems of Ecology |date=19 August 2015 |volume=8 |issue=4 |pages=523–533 |doi=10.1134/S199542551504006X|s2cid=16291866 }}
* {{cite journal |last1=Freitas |first1=L. |last2=Sosa|first2=M.|title=Floral Biology and Pollination Mechanisms in Two Viola Species-From Nectar to Pollen Flowers? |journal=[[Annals of Botany]] |date=19 December 2002 |volume=91 |issue=3 |pages=311–317 |doi=10.1093/aob/mcg025|pmid=12547683|pmc=4244963}}
* {{cite journal |last1=Hildebrandt |first1=U. |last2=Kaldorf |first2=M. |last3=Bothe |first3=H. |title=The Zinc Violet and its Colonization by Arbuscular Mycorrhizal Fungi |journal=[[Journal of Plant Physiology]] |date=May 1999 |volume=154 |issue=5–6 |pages=709–717 |doi=10.1016/S0176-1617(99)80249-1|ref={{harvid|Hildebrandt et al|1999}}}}
* {{cite journal |last1=Kopper |first1=Brian J. |last2=Charlton |first2=Ralph E. |last3=Margolies |first3=David C. |title=Oviposition Site Selection by the Regal Fritillary, Speyeria idalia, as Affected by Proximity of Violet Host Plants|journal=Journal of Insect Behavior |date=2000 |volume=13 |issue=5 |pages=651–665 |doi=10.1023/A:1007887809621|s2cid=19315345 |ref={{harvid|Kopper et al|2000}}}}
* {{cite journal |last1=Łańcucka-Środoniowa |first1=Maria |title=Macroscopic plant remains from the freshwater Miocene of the Nowy Sącz Basin (West Carpathians, Poland) |journal=Acta Palaeobotanica |date=1979 |volume=20 |issue=1 |pages=3–117 |url=http://bomax.botany.pl/cgi-bin/pubs/data/article_pdf?id=2798 }}
* {{cite journal |last1=Lord |first1=E. M. |title=Cleistogamy: A tool for the study of floral morphogenesis, function and evolution |journal=[[The Botanical Review]] |date=October 1981 |volume=47 |issue=4 |pages=421–449 |doi=10.1007/BF02860538|jstor=4353990|s2cid=19754210 }}
*{{cite journal|last1=Park|first1=Sungkyu|display-authors=etal|title=Cyclotide evolution: Insights from the analyses of their precursor sequences, structures and distribution in Violets (Viola)|journal=Frontiers in Plant Science|year=2017|volume=8|pages=92–110|doi=10.3389/fpls.2017.02058|pmid=29326730|pmc=5741643|doi-access=free}} 
* {{cite journal|last=Saint-Hilaire|first=Augustin|author-link=Augustin Saint-Hilaire|title=Tableau monographique des plantes de la flore du Brésil méridional appartenant au groupe (classe Br.) qui comprend qui comprend les Droséracées, les Violacées, les Cistinées et les Frankenicées: Violacées|journal=Annales du museum national d'histoire naturelle|volume=72|pages=445–498|url=https://books.google.com/books?id=ouJaAAAAcAAJ|year=1824|language=fr}}
* {{cite journal |last1=Shuey |first1=John |last2=Jacquart |first2=Ellen |last3=Orr |first3=Stuart |last4=Becker |first4=Fiona |last5=Nyberg |first5=Alyssa |last6=Littiken |first6=Robert |last7=Anchor |first7=Ted |last8=Luchik |first8=Derek |title=Landscape-scale response to local habitat restoration in the regal fritillary butterfly (Speyeria idalia) (Lepidoptera: Nymphalidae) |journal=Journal of Insect Conservation |date=9 September 2016 |volume=20 |issue=5 |pages=773–780 |doi=10.1007/s10841-016-9908-4|s2cid=25321534 |ref={{harvid|Shuey et al|2016}}}}
* {{cite journal |last1=Thiele |first1=Kevin R |last2=Prober |first2=Suzanne M |title=New species and a new hybrid in the Viola hederacea species complex, with notes on Viola hederacea Labill. |journal=[[Muelleria (journal)|Muelleria]] |date=2003 |volume=18 |pages=7–25 |doi=10.5962/p.254920 |s2cid=251005673 |url=https://www.researchgate.net/publication/268277479 |doi-access=free }}
* {{cite journal |last1=Tikhomirov |first1=V. N |title=A revision of the genus Viola section Plagiostigma (Violaceae) in Republic of Belarus. |journal=Botanicheskiĭ Zhurnal |date=2015 |volume=100 |issue=5 |pages=490–500 |url=https://www.cabi.org/ISC/abstract/20153338855 |language=ru |access-date=2020-03-17 |archive-date=2020-03-17 |archive-url=https://web.archive.org/web/20200317203452/https://www.cabi.org/ISC/abstract/20153338855 |url-status=dead }}
* {{cite journal |last1=Yockteng |first1=R. |last2=Jr Ballard |first2=H. E. |last3=Mansion |first3=G. |last4=Dajoz |first4=I. |last5=Nadot |first5=S. |title=Relationships among pansies ( Viola section Melanium ) investigated using ITS and ISSR markers |url=https://www.researchgate.net/publication/225488190 |jstor=23645153 |journal=[[Plant Systematics and Evolution]] |date=1 November 2003 |volume=241 |issue=3–4 |pages=153–170 |doi=10.1007/s00606-003-0045-7 |ref={{harvid|Yockteng et al|2003}} |citeseerx=10.1.1.721.5590 |s2cid=25104565 }}
* {{cite journal |last1=Wahlert |first1=Gregory A. |last2=Marcussen |first2=Thomas |last3=de Paula-Souza |first3=Juliana |last4=Feng |first4=Min |last5=Ballard |first5=Harvey E. |title=A Phylogeny of the Violaceae (Malpighiales) Inferred from Plastid DNA Sequences: Implications for Generic Diversity and Intrafamilial Classification |url=https://www.researchgate.net/publication/256545045 |journal=[[Systematic Botany]] |date=1 March 2014 |volume=39 |issue=1 |pages=239–252 |doi=10.1600/036364414X678008 |s2cid=86452033 |ref={{harvid|Wahlert et al|2014}} }}
* {{cite journal |last1=Watson |first1=John M. |last2=Flores |first2=R. |title=A new name in section Andinium W.becker of the genus Viola L. (Violaceae) |journal=[[Gayana. Botánica]] |date=2003 |volume=60 |issue=2 |doi=10.4067/S0717-66432003000200009|doi-access=free }}
* {{cite journal |last1=Watson |first1=John M. |last2=Flores |first2=Ana R. |last3=Arroyo-Leuenberger |first3=Silvia C. |title=A new Viola (Violaceae) from the Argentinian Andes |journal=[[Willdenowia (journal)|Willdenowia]] |date=25 March 2019 |volume=49 |issue=1 |pages=35 |doi=10.3372/wi.49.49105|doi-access=free|ref={{harvid|Watson et al|2019}}}}
* {{cite journal |last1=Watson |first1=John |last2=Watson |first2=Anita |title=Fire and Ice: Rosulate Viola Evolution Part One – The Stage is Set |journal=North American Rock Garden Society Quarterly |date=Fall 2012 |volume=70 |issue=4 |pages=360–366 |url=https://nargs.org/sites/default/files/free-rgq-downloads/roga_70-4.pdf }}
* {{cite journal |last1=Yoo |first1=Ki-Oug |last2=Jang |first2=Su-Kil |title=Infrageneric relationships of Korean Viola based on eight chloroplast markers |journal=Journal of Systematics and Evolution |date=November 2010 |volume=48 |issue=6 |pages=474–481 |doi=10.1111/j.1759-6831.2010.00102.x|doi-access=free}}
* {{cite journal | last1=Zhou | first1=J. S. | display-authors=etal | year=2008 | title=''Viola nanlingensis'' (Violaceae), a new species from Guangdong, southern China | url=http://www.sekj.org/PDF/anb45-free/anb45-233.pdf | journal=Annales Botanici Fennici | volume=45 | issue=3 | pages=233–36 | doi=10.5735/085.045.0312 | s2cid=84616726 }}

====Phylogeny and taxonomy====
* {{cite journal |last1=Ballard |first1=Harvey E. |last2=Sytsma |first2=Kenneth J. |title=Evolution And Biogeography Of The Woody Hawaiian Violets (Viola, Violaceae): Arctic Origins, Herbaceous Ancestry And Bird Dispersal |url=http://sytsma.botany.wisc.edu/pdf/Ballard00.pdf |archive-url=https://web.archive.org/web/20200930001501/http://sytsma.botany.wisc.edu/pdf/Ballard00.pdf |url-status=live |archive-date=September 30, 2020 |journal=[[Evolution (journal)|Evolution]] |date=October 2000 |volume=54 |issue=5 |pages=1521–1532 |doi=10.1111/j.0014-3820.2000.tb00698.x |pmid=11108581 |s2cid=10320278 |doi-access=free }}
* {{cite journal |last1=Ballard |first1=Harvey E. |last2=Sytsma |first2=Kenneth J. |last3=Kowal |first3=Robert R. |title=Shrinking the Violets: Phylogenetic Relationships of Infrageneric Groups in Viola (Violaceae) Based on Internal Transcribed Spacer DNA Sequences |url=http://sytsma.botany.wisc.edu/pdf/Ballard99.pdf |journal=[[Systematic Botany]] |date=October 1998 |volume=23 |issue=4 |pages=439 |doi=10.2307/2419376 |jstor=2419376 |ref={{harvid|Ballard et al|1998}} }}
* {{cite journal|last1=Ballard|first1=Harvey E|last2=Iltis|first2=Hugh H|title=''Viola lilliputana'' sp. nov. (''Viola'' sect. ''Andinium'', Violaceae), one of the world's smallest violets, from the Andes of Peru|url=https://www.researchgate.net/publication/257776309|year=2012|journal=[[Brittonia]]|volume=64|issue=4|pages=353–358|doi=10.1007/s12228-012-9238-0|s2cid=14344961}}
* {{cite journal |last1=Chervin |first1=Justine |last2=Talou |first2=Thierry |last3=Audonnet |first3=Marjorie |last4=Dumas |first4=Bernard |last5=Camborde |first5=Laurent |last6=Esquerré-Tugayé |first6=Marie-Thérèse |last7=Roux |first7=Christophe |last8=Cabanac |first8=Guillaume |last9=Marti |first9=Guillaume |title=Deciphering the phylogeny of violets based on multiplexed genetic and metabolomic approaches |url=https://www.irit.fr/publis/IRIS/2019_Phytochemistry_CTADCETRCM.pdf |journal=[[Phytochemistry (journal)|Phytochemistry]] |date=July 2019 |volume=163 |pages=99–110 |doi=10.1016/j.phytochem.2019.04.001 |pmid=31035059 |bibcode=2019PChem.163...99C |ref={{harvid|Chervin et al|2019}} |doi-access=free }}
* {{cite journal |last1=Danihelka |first1=Jiří |display-authors=etal |title=Viola montana and V. persicifolia (Violaceae): Two names to be rejected |journal=[[Taxon (journal)|Taxon]] |date=December 2010 |volume=59 |issue=6 |pages=1869–1878 |doi=10.1002/tax.596019 |jstor=41059881 |url=https://www.researchgate.net/publication/233614694 }}
* {{cite journal |last1=Fan |first1=Qiang |last2=Chen |first2=Sufang |last3=Wang |first3=Longyuan |last4=Chen |first4=Zaixiong |last5=Liao |first5=Wenbo |title=A new species and new section of Viola (Violaceae) from Guangdong, China |journal=[[Phytotaxa]] |date=4 February 2015 |volume=197 |issue=1 |pages=15 |doi=10.11646/phytotaxa.197.1.2|doi-access=free|ref={{harvid|Fan et al|2015}}}}
* {{cite journal |last1=Gingins |first1=F de |author-link=Frédéric Charles Jean Gingins de la Sarraz |title=Mémoires sur la Famille des Violacees |journal=Mémoires de la Société de Physique et d'Histoire Naturelle de Genève |date=1823 |volume=2 |issue=1 |pages=1–27 |url=https://www.biodiversitylibrary.org/item/39748#page/9/mode/1up }}
* {{cite journal |last1=Gonzáles |first1=Paúl |last2=Cano |first2=Asunción |title=Two new species of Viola (Violaceae) named in honor of preceding Peruvian botanists |journal=[[Phytotaxa]] |date=2 November 2016 |volume=283 |issue=1 |pages=83–90 |doi=10.11646/phytotaxa.283.1.6}}
* {{cite journal |last1=Magrini |first1=Sara |last2=Scoppola |first2=Anna |title=Further studies in Viola Sect. Melanium (Violaceae). Identity and typification of Viola nana and V. henriquesii, two neglected European Atlantic taxa |url=https://digitale.cbnbl.org/documents/g6847.pdf |journal=[[Phytotaxa]] |date=13 October 2015 |volume=230 |issue=3 |pages=259 |doi=10.11646/phytotaxa.230.3.4 }}
* {{cite journal |last1=Małobęcki |first1=Andrzej |last2=Marcussen |first2=Thomas |last3=Bohdanowicz |first3=Jerzy |last4=Migdałek |first4=Grzegorz |last5=Słomka |first5=Aneta |last6=Kuta |first6=Elżbieta |title=Cleistogamy and phylogenetic position of Viola uliginosa (Violaceae) re-examined |journal=[[Botanical Journal of the Linnean Society]] |date=September 2016 |volume=182 |issue=1 |pages=180–194 |doi=10.1111/boj.12460|ref={{harvid|Malobecki et al|2016}}|doi-access=free }}
* {{cite journal |last1=Marcussen |first1=Thomas |last2=Oxelman |first2=Bengt |last3=Skog |first3=Anna |last4=Jakobsen |first4=Kjetill S |title=Evolution of plant RNA polymerase IV/V genes: evidence of subneofunctionalization of duplicated NRPD2/NRPE2-like paralogs in Viola (Violaceae) |journal=[[BMC Evolutionary Biology]] |date=2010 |volume=10 |issue=1 |pages=45 |doi=10.1186/1471-2148-10-45|pmid=20158916 |pmc=2834690 |ref={{harvid|Marcussen et al|2010}} |doi-access=free }}
* {{cite journal |last1=Marcussen |first1=Thomas |last2=Jakobsen |first2=Kjetill S. |last3=Danihelka |first3=Jiří |last4=Ballard |first4=Harvey E. |last5=Blaxland |first5=Kim |last6=Brysting |first6=Anne K. |last7=Oxelman |first7=Bengt |title=Inferring Species Networks from Gene Trees in High-Polyploid North American and Hawaiian Violets (Viola, Violaceae) |journal=[[Systematic Biology (journal)|Systematic Biology]] |date=January 2012 |volume=61 |issue=1 |pages=107–126 |doi=10.1093/sysbio/syr096|pmid=21918178 |pmc=3243738 |doi-access=free|ref={{harvid|Marcussen et al|2012}}}}
* {{cite journal |last1=Marcussen |first1=Thomas |last2=Heier |first2=Lise |last3=Brysting |first3=Anne K. |last4=Oxelman |first4=Bengt |last5=Jakobsen |first5=Kjetill S. |title=From Gene Trees to a Dated Allopolyploid Network: Insights from the Angiosperm Genus Viola (Violaceae) |journal=[[Systematic Biology (journal)|Systematic Biology]] |date=January 2015 |volume=64 |issue=1 |pages=84–101 |doi=10.1093/sysbio/syu071|doi-access=free|pmid=25281848|pmc=4265142|ref={{harvid|Marcussen et al|2015}}}}
* {{cite journal | last1=Ning | first1=Z. L. | display-authors=etal | year=2012 | title=''Viola jinggangshanensis'' (Violaceae), a new species from Jiangxi, China | url=http://www.annbot.net/PDF/anb49-free/anb49-383i.pdf | journal=Annales Botanici Fennici | volume=49 | issue=5 | pages=383–86 | doi=10.5735/085.049.0610 | s2cid=85568012 }}
* {{cite journal |last1=Mohammadi Shahrestani |first1=Maryam |last2=Saeidi Mehrvarz |first2=Shahryar |last3=Marcussen |first3=Thomas |last4=Yousefi |first4=Narjes |title=Taxonomy and comparative anatomical studies of Viola sect. Sclerosium (Violaceae) in Iran |journal=[[Acta Botanica Gallica]] |date=5 August 2014 |volume=161 |issue=4 |pages=343–353 |doi=10.1080/12538078.2014.932702|doi-access=free|ref={{harvid|Shahrestani et al|2014}}}}
* {{cite journal |last1=Whang |first1=Sung Soo |title=A taxonomic study of Viola section Chamaemelanium in Korea-based on morphological characters |journal=Korean Journal of Plant Taxonomy |date=31 December 2002 |volume=32 |issue=4 |pages=397–416 |doi=10.11110/kjpt.2002.32.4.397 |url=https://www.researchgate.net/publication/323803706 }}
* {{cite journal|last=Wittrock|first=Veit Brecher|author-link=Veit Brecher Wittrock|title=Viola-studier I. Morfologisk-biologiska och systematiska studier öfver Viola tricolor (L.) och hennes närmare anförvandter|journal=Acta Horti Bergiani: Meddelanden Från Kongl. Svenska Vetenskaps-Akademiens Trädgård Bergielund|url=https://books.google.com/books?id=ExUYAAAAYAAJ|volume=2|issue=1|year=1892–1897|language=sv}}{{link note|note=also available [https://www.biodiversitylibrary.org/item/86025#page/7/mode/1up here] at [[Biodiversity Heritage Library|BHL]]}}
* {{cite journal|last=Wittrock|first=Veit Brecher|author-link=Veit Brecher Wittrock|author-mask=1|title=Viola-studier II. Bidrag till de odlade penséernas historia med särskild hänsyn till deras härkomst|journal=Acta Horti Bergiani: Meddelanden Från Kongl. Svenska Vetenskaps-Akademiens Trädgård Bergielund|url=https://books.google.com/books?id=ExUYAAAAYAAJ|volume=2|issue=7|year=1892–1897a|language=sv}}{{link note|note=also available [https://www.biodiversitylibrary.org/item/86025#page/441/mode/1up here] at [[Biodiversity Heritage Library|BHL]]}}

====Encyclopaedias====
* {{cite encyclopedia |last1=Hosch |first1=William L. |title=Viola |url=https://www.britannica.com/plant/Viola-plant-genus |publisher=[[Encyclopædia Britannica]] |access-date=6 March 2020 |date=23 April 2008 }}
* {{cite EB1911|wstitle=Violet|short=x}}
* {{cite NSRW|wstitle=Violets|short=x}}

===Websites===
* {{cite web |title=Viola |url=https://www.biolib.cz/en/taxon/id38844/ |website=BioLib: Biological library |access-date=28 February 2020 |date=2019 |ref={{harvid|BioLib|2019}} }} (''taxonomy'')
** {{cite web |title=Viola capillaris Pers. |url=https://www.biolib.cz/en/taxon/id418060/ |access-date=19 March 2020 |ref={{harvid|V capillaris|2020}} }}
* {{cite web |title=American Violet Society |url=http://www.americanvioletsociety.org/index.htm |access-date=1 March 2020 |date=2007 |ref={{harvid|AVS|2007}} |archive-date=19 February 2020 |archive-url=https://web.archive.org/web/20200219080019/http://www.americanvioletsociety.org/index.htm |url-status=dead }}
* {{cite web |title=Viola 'Little David' (Vtta) |url=https://www.rhs.org.uk/Plants/83544/Viola-Little-David-(Vtta)/Details |website=Plants |publisher=[[Royal Horticultural Society]] |access-date=4 March 2020 |date=2020 |ref={{harvid|RHS Little David|2020}} }}
* {{cite web |title=Viola 'Königin Charlotte' (Vt) |url=https://www.rhs.org.uk/Plants/215144/Viola-Konigin-Charlotte-(Vt)/Details |website=Plants |publisher=[[Royal Horticultural Society]] |access-date=4 March 2020 |date=2020 |ref={{harvid|RHS Konigin Charlotte|2020}} }}
* {{cite web |title=Violet, Common Blue (Viola papilionacea) |url=http://www.voyageurcountry.com/htmls/floweringplants/plants/violetblue.html |website=Voyageur Country: Flowering plants |access-date=6 March 2020 |date=2020 |ref={{harvid|VC|2020}} }}
* {{cite web |title=Natural history and research on Viola cazorlensis |url=http://ebd06.ebd.csic.es/organisms/vcazorlensis/Vcazorlensis.html |website=Alonso-Herrera Lab |publisher=[[Spanish National Research Council]] (CSIC) |access-date=10 March 2020 |ref={{harvid|CSIC|2020}} |archive-date=5 February 2021 |archive-url=https://web.archive.org/web/20210205175843/http://ebd06.ebd.csic.es/organisms/vcazorlensis/Vcazorlensis.html |url-status=dead }}
* {{cite web |last1=Kelly |first1=R.O. |last2=Deng |first2=Z. |last3=Harbaugh |first3=B.K. |title=Evaluation of Viola Cultivars as Bedding Plants for Florida |url=http://ufdcimages.uflib.ufl.edu/IR/00/00/17/73/00001/EP32700.pdf |website=Electronic Data Information Source (EDIS) |publisher=Environmental Horticulture Department, Florida Cooperative Extension Service, [[Institute of Food and Agricultural Sciences]], [[University of Florida]] |access-date=25 March 2020 |date=October 2007 |ref={{harvid|Kelly et al|2007}} |archive-date=7 March 2025 |archive-url=https://web.archive.org/web/20250307202432/http://ufdcimages.uflib.ufl.edu/IR/00/00/17/73/00001/EP32700.pdf |url-status=dead }}
* {{cite web |title=AGM Plants (Ornamental) |url=https://www.rhs.org.uk/plants/pdfs/agm-lists/agm-ornamentals.pdf |access-date=26 March 2020 |pages=109–110 |date=November 2018 |publisher=[[Royal Horticultural Society]] |ref={{harvid|RHS|2018}} }}

;Databases
* {{cite web|last=WFO|author-link=World Flora Online|title=Viola L.|url=http://www.worldfloraonline.org/taxon/wfo-4000040312|website=World Flora Online|access-date=27 February 2020|date=2019}}
* {{cite web |last=POTWO |title=Viola L. |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30000540-2 |website=[[Plants of the World Online]] |publisher=[[Royal Botanic Gardens, Kew]] |access-date=6 March 2020 |ref={{harvid|POTWO|2020}} }}
* {{cite web|last=IPNI|author-link=International Plant Names Index|title=Viola L., Genera Plantarum ed. 5 (1754)|url=https://www.ipni.org/n/120884-3|publisher=[[Royal Botanic Gardens, Kew]]|access-date=7 March 2020|ref={{harvid|IPNI|2020}}}}
* {{cite web|last1=Little|first1=R. John|last2=McKinney|first2=Landon E.|title=Viola|url=http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=134607|work=[[Flora of North America]]|year=2003|volume=6|access-date=1 March 2020|publisher=[[Oxford University Press]]|location=New York}}
* {{cite web |last1=Paula-Souza |first1=Juliana de |last2=Ballard |first2=Harvey E. |title=Neotropical Violaceae |url=https://www.kew.org/science/tropamerica/neotropikey/families/Violaceae.htm |website=Neotropikey: Interactive key and information resources for flowering plants of the Neotropics |publisher=[[Royal Botanic Gardens, Kew]] |access-date=18 April 2020 |date=2009 }}
* {{cite web |last1=Fu |first1=Kunjun |last2=Ohba |first2=Hideaki |last3=Gilbert |first3=Michael G. |title=Viola Linnaeus, Sp. Pl. 2: 933. 1753 |url=http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=134607 |pages=72, 74 |access-date=3 March 2020 |year=2004 |ref={{harvid|Fu et al|2004}} }}, {{link note|note=in [[Flora of China (series)|Flora of China online]] vol. 13}}
* {{cite web |editor-last1=Karlsson |editor-first1=Thomas |editor-last2=Marcussen |editor-first2=Thomas |title=Viola L. |url=http://www.floranordica.org/Review/-Review_public/accounts/Viola.html |archive-url=https://web.archive.org/web/20160731183619/http://floranordica.org/Review/-Review_public/accounts/Viola.html |url-status=usurped |archive-date=July 31, 2016 |website=Flora Nordica 6 |date=2010 }}
* {{cite web |title=Viola Horticultural Classification |url=http://www.rhs.org.uk/RHSPlantFinder/GenusClass.asp?Genus=Viola |website=RHS Plant Finder: Genus |publisher=[[Royal Horticultural Society]] |access-date=4 March 2020 |archive-url=https://web.archive.org/web/20090708035929/http://www.rhs.org.uk/RHSPlantFinder/GenusClass.asp?Genus=Viola |archive-date=8 July 2009 |date=2009 |ref={{harvid|RHS|2009}} }}
* {{cite web |title=Violaceae |url=https://en.wikibooks.org/wiki/Flora_of_New_York/Violaceae |website=[[Wikibooks]]: Flora of New York |publisher=[[Wikimedia]] |access-date=4 March 2020 |ref={{harvid|FNY|2020}} }}

;Images
* {{cite web |last1=Rein |first1=Pasi |last2=Repo |first2=Paula |title=Violaceae |url=http://www.topwalks.net/plants/generos/violaceae.htm |website=Walking routes in Spain - Plants |access-date=28 February 2020 }}
* {{cite web |title=Violaceae |url=http://www.alpine-plants-jp.com/art/index_sumireka_apg3_210.htm |website=Wild herbs and Alpine Plants, Japan |publisher=Flavon's Art Gallery |access-date=28 February 2020 |date=2020 }}
* {{cite web |title=Violaceae |url=http://www.botanische-spaziergaenge.at/viewforum.php?f=384 |website=Botanische-spaziergaenge: Bilder von Österreichs Flora |access-date=1 March 2020 |language=de }}
* {{cite web |title=Violets (Genus Viola) |url=https://inaturalist.ca/taxa/50829-Viola |website=[[iNaturalist]] |publisher=[[National Geographic Society]] |access-date=2 March 2020 }} ''includes maps''
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[[Category:Viola (plant)| ]]
[[Category:Violaceae genera]]
[[Category:Garden plants]]
[[Category:Leaf vegetables]]
[[Category:Medicinal plants]]