Juncus

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Juncus is a genus of monocotyledonous flowering plants, commonly known as rushes. It is the largest genus in the family Juncaceae,<ref name="FNA">Template:Cite book</ref> containing around 340 species.<ref name = powo/>

Description

Rushes of the genus Juncus are herbaceous plants that superficially resemble grasses or sedges.<ref name="Yakandawala">Template:Cite journalTemplate:Dead link</ref> They have historically received little attention from botanists; in his 1819 monograph, James Ebenezer Bicheno described the genus as "obscure and uninviting".<ref>Template:Cite journal</ref>

The form of the flower differentiates rushes from grasses or sedges. The flowers of Juncus comprise five whorls of floral parts: three sepals, three petals (or, taken together, six tepals), two to six stamens (in two whorls) and a stigma with three lobes.<ref name="Yakandawala"/> The stems are round in cross-section, unlike those of sedges,<ref name="Yakandawala"/> which are typically somewhat triangular in cross-section.<ref>Template:Cite book</ref>

In Juncus section Juncotypus (formerly called Juncus subg. Genuini),<ref name="Kirschner"/> which contains some of the most widespread and familiar species, the leaves are reduced to sheaths around the base of the stem and the bract subtending the inflorescence closely resembles a continuation of the stem, giving the appearance that the inflorescence is lateral.<ref>Template:Cite journal</ref>

Distribution and ecology

Juncus has a cosmopolitan distribution, with species found throughout the world, with the exception of Antarctica.<ref name="FNA"/> They typically grow in cold or wet habitats, and in the tropics, are most common in montane environments.<ref name="Yakandawala"/>

Fossil record

Several fossil fruits of a Juncus species have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.<ref>Angiosperm Fruits and Seeds from the Middle Miocene of Jutland (Denmark) by Else Marie Friis, The Royal Danish Academy of Sciences and Letters 24:3, 1985</ref>

Classification

In Juncus effusus (and other species in J. sect. Juncotypus), the bract appears as a continuation of the stem, and the inflorescence appears lateral.

The genus Juncus was first named by Carl Linnaeus in his 1753 Template:Lang. The type species of the genus was designated by Frederick Vernon Coville, who in 1913 chose the first species in Linnaeus' account, Juncus acutus.<ref name="Kirschner"/> Juncus can be divided into two major groups, one group with cymose inflorescences that include bracteoles, and one with racemose inflorescences with no bracteoles.<ref name="Kirschner"/>

In 2013 the genus Oreojuncus was separated from Juncus. In 2022 Viktorie Brožová et al. published a phylogenetic analysis of the cyperids (families Juncaceae, Cyperaceae, and Thurniaceae) which found Juncus to be paraphyletic, and the authors proposed that six new genera, Alpinojuncus, Agathryon, Australojuncus, Boreojuncus, Juncinella, and Verojuncus, be split from Juncus.<ref>Viktorie Brožová, Jarosław Proćków, Lenka Záveská Drábková, Toward finally unraveling the phylogenetic relationships of Juncaceae with respect to another cyperid family, Cyperaceae. Molecular Phylogenetics and Evolution, Volume 177, 2022, 107588, ISSN 1055-7903, https://doi.org/10.1016/j.ympev.2022.107588.</ref> As of July 2025 Plants of the World Online accepts Juncinella but treats the others as synonyms of Juncus.<ref name = powo/>

The genus is divided into the following subgenera and sections:<ref name="Kirschner">Template:Cite journal</ref>

Species

Template:Multiple image As of July 2025, Plants of the World Online accepts 342 species:<ref name=powo/>

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References

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