Rorippa

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Rorippa is a globally distributed genus in the family Brassicaceae, with species occurring on all continents except for Antarctica.<ref name=":1">Template:Cite book</ref><ref name=":2">Template:Cite journal</ref><ref name=":0">Template:Cite journal</ref> Rorippa species are natively distributed in the Northern Hemisphere through Eurasia and North America, and dispersed into the Southern Hemisphere through long-distance dispersal.<ref name=":0" /> Rorippa species are annual to perennial herbs, usually with yellow flowers and a peppery flavour. They are known commonly as yellowcresses.

Description

As a close relative of Arabidopsis, Rorippa has emerged as a group of valuable model organisms for investigating various biological processes. Researchers have utilized Rorippa to study developmental phenomena such as heterophylly,<ref name=":4">Template:Cite journal</ref><ref name=":5">Template:Cite journal</ref> weediness,<ref name=":6">Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name=":7">Template:Cite journal</ref> and vegetative regeneration.<ref>Template:Cite journal</ref><ref name=":8">Template:Cite journal</ref><ref>Template:Cite journal</ref> For example, heterophylly is the ability of plants to produce different leaf forms in response to contrasting environments, such as aerial or submerged conditions. This may incur anatomical or physiological changes and facilitate adaptation to the amphibious lifestyle in Rorippa,<ref name=":9">Template:Cite journal</ref>

Additionally, Rorippa has been employed to explore stress tolerance mechanisms, including responses to submergence,<ref name=":10">Template:Cite journal</ref><ref name=":11">Template:Cite journal</ref><ref name=":12">Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref name=":9" /><ref name=":13">Template:Cite journal</ref> heavy metals,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> high-altitudes,<ref name=":14">Template:Cite journal</ref><ref name=":15">Template:Cite journal</ref> and herbivory (specifically the mustard aphid).<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> For example, Rorippa amphibia can escape submergence through elongation,<ref name=":11" /> while Rorippa sylvestris or Rorippa palustris can photosynthesize underwater and exhibits a hyponastic response (positive growth response to gravity), demonstrating a quiescence strategy (a period of reduced activity during unfavorable conditions).<ref name=":11" /><ref name=":12" />

Furthermore, Rorippa has served as a model system for studying biological invasion, with research focusing on evolutionary,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> ecological,<ref name=":3" /><ref>Template:Cite journal</ref> and historical aspects.<ref name=":1" /><ref name=":16">Template:Cite journal</ref><ref name=":17">Template:Cite journal</ref><ref name=":18">Template:Cite journal</ref><ref name=":19">Template:Cite journal</ref>

Ecology

Most Rorippa species thrive in moist or wet environments like ditches, meadows, waterfronts, and wetlands,<ref name=":3">Template:Cite book</ref> highlighting their exceptional tolerance to flooding.<ref name=":10" /> This facilitates the dispersal of their seeds or vegetative propagules by floods over short to long ranges. For example, their fruits with seeds can remain viable for up to 60 days while floating in water.<ref name=":3" /> The aquatic or marshy habitats of Rorippa often overlap with those of migratory shorebirds,<ref name=":2" /> which could potentially carry seeds or fragments over long distances, establishing new populations far from the source. Furthermore, several adaptations, like the mucilage coating or hollows on their seeds, and their ability to self-fertilize and reproduce clonally,<ref name=":1" /> might also contribute to their long-distance dispersal.<ref name=":0" />

Rorippa species are known for colonizing disturbed or wet areas first. They serve as valuable indicators of hydrophytic (water-loving) vegetation types. According to the National Wetland Plant List (NWPL) for the United States, several Rorippa species are classified as wetland indicators, with a high probability of occurring in Obligate (OBL) or Facultative Wetland (FACW) categories. For instance, nearly 55% of the 22 North American Rorippa species are categorized as OBL wetland indicators,<ref name=":3" /> highlighting their strong association with wet environments. This characteristic makes Rorippa plants a valuable tool for wetland establishment, restoration, and enhancement efforts.

Example

Rorippa aquatica, a North American lakecress, is a valuable model organism for studying plant development and adaptation. It exhibits striking heterophylly,<ref name=":4" /><ref name=":5" /><ref name=":13" /> altering its leaf shape in response to environmental conditions like submergence, temperature, and light. In low-light submerged environments, for example, it develops finely dissected leaves. While in terrestrial conditions, it forms simple leaves with serrated edges. This leaf shape variation is controlled by the levels of plant hormones including gibberellin (GA) and ethylene, as well as the expression of specific genes, such as KNOX1<ref name=":5" /> or RaSPCH/RaMUTE,<ref name=":13" /> providing an efficient way for leaves to absorb sunlight underwater. The species is also used to study vegetative propagation as it can regenerate from leaf fragments.<ref name=":8" /> Its close phylogenetic relationship to Arabidopsis thaliana and its recently sequenced allotetraploid genome make it a powerful tool for genetic and genomic research.<ref>Template:Cite journal</ref>

Rorippa elata is a type of plant that has adapted to live in high-altitude mountain environments. It can adjust its traits, like flowering time and chemical defenses, to survive in different conditions.<ref name=":15" /> The plant's ability to adapt is also linked to its polyploid nature, which seems to have played a role in its successful colonization of high-altitudes during periods of historical climate change.<ref name=":14" />

Rorippa palustris, a short-lived and self-pollinating herb, is a ruderal weed that has expanded into disturbed wetland areas across the world. A key characteristic of R. palustris, and other ruderal plants, is its short life cycle.<ref name=":7" /><ref name=":14" /> Genetic studies have shown that mutations in the CRY2 gene contribute to this early-flowering trait.<ref name=":6" /> These mutations lead to a constitutively active CRY2 protein, which overrides the need for vernalization (a cold period) and allows the plant to flower early, even under short-day conditions.

List of species

There are about 75<ref name="china">Rorippa. Flora of China.</ref> to 87<ref>Rorippa. The Jepson eFlora 2013.</ref><ref name="fna">Rorippa. Flora of North America.</ref> species in the genus. About 70% of Rorippa are polyploids, and 90% of them are endemic to specific continents.<ref name=":0" /> A few of Rorippa species are widely distributed and invasive, including Rorippa amphibia, Rorippa dubia, Rorippa indica, Rorippa palustris, and Rorippa sylvestris. Plants of Rorippa palustris can be found globally, making it one of the most successful weeds in the world.