The following Participating Institutions are custodians for this species in the CPC National Collection:
Rancho Santa Ana Botanic Garden
Santa Barbara Botanic Garden
The conservation of Rorippa gambelii is fully sponsored.
Dieter Wilken contributed to this Plant Profile.
Once found from San Luis Obispo County south to San Bernardino County, California, and in central Mexico, Gambels watercress today is known from only three localities in the United States, and its numbers have dwindled to perhaps less than 300 individuals. Known from about 8 occurrences in the United States at the time it was listed in 1993, the number of extant populations has dwindled to only three in southern San Luis Obispo County and western Santa Barbara County (Anonymous 2008a; Parikh et al. 1998). At one of these localities, it co-occurs with marsh sandwort (Arenaria paludicola), another endangered species. The last and only report made for San Bernardino County was in 1935 at Urbita Hot Springs, currently the site of a mall next to the Orange Show Fairgrounds in San Bernardino. An early report from the mountains of San Diego County has not been confirmed (Anonymous 2008b). Although reported from Mexico, its status there is unknown (Wickenheiser, L.P. 1989). Gambels watercress (Rorippa gambelii, Cardamine gambelii in literature) is probably best treated as a species of Nasturtium (Al-Shehbaz and Price 1998).
Gambels water cress is an aquatic, herbaceous perennial, producing floating and emergent stems (Abrams and Ferris 1944; Mason 1957; Rollins 1993; Al-Shehbaz and Price, 1998). Vegetative shoots often sprawl over associated vegetation and have been reported to reach up to 1 meter in length, bearing pinnately compound leaves. Vegetative shoots can spread and produce new plants adventitiously. The flowering shoots produce terminal clusters of white flowers. Flowers are about 1 cm wide at anthesis, and bear the 4 white petals and 6 stamens typical of a mustard. Each fruit can produce up to 20 seeds, which are yellowish- to reddish brown in color. Flowering ranges from April through July. Plants of Gambels watercress have been confused with the introduced watercress (Rorippa nasturtium-aquaticum = Nasturtium officinale). These two species are also known to hybridize at one remaining occurrence, making identification more difficult, and also resulting in a potential threat from the apparently more competitive hybrid.
Distribution & Occurrence
Gambels watercress occurs naturally in open or semi-shaded sites along the edges of permanent, slow-moving streams and at the edges of freshwater marshes or lakes. The typical substrate is sandy, saturated, and with a high organic content. Gambels watercress has been associated with such riparian species as bur-reed (Sparganium), tules (Scirpus), rushes (Juncus), cattails (Typha), wax myrtle (Myrica californica), reed-grass (Calamagrostis), and arroyo willow (Salix lasiolepis). Observations of its growth at the Santa Barbara Botanic Garden confirm its need for a constant source of fresh water. Studies of soil seed banks at one locality demonstrated a viable natural seed bank, based on observations of germinating seedlings, but seed age could not be determined (Mazer and Waddell 1994; Mazer 2000).
|Among approximately 8 historic occurrences, only three are believed to be extant. As recently as 1998, the number of individual plants at extant sites was collectively estimated to be fewer than 1000 flowering shoots (Anonymous 2008b). However, the number of genetically distinct plants remains unknown, and probably are fewer.|
Conservation, Ecology & Research
Competition from alien invasives.
Hybridization with the common European watercress (Nasturtium officinale).
Eutrophication resulting from increased nutrient levels.
Studies of plants at the Santa Barbara Botanic Garden have provided mixed results regarding the breeding system. Overall, flowers are self-compatible, but seed set, relative to a larger number of ovules, is enhanced by augmented pollination, suggesting that visitation by insects are important to pollination in nature
Field studies of potential suitable habitat are being conducted by the US Fish and Wildlife Service.
The Santa Barbara Botanic Garden maintains a living collection of plants representing limited genetic diversity from one natural population and seed collections secured from one other occurrence, currently believed extirpated.
The number of distinct genetic strains needs to be estimated, using molecular markers.
Abrams, L.; Ferris, R.S. 1944. Illustrated flora of the Pacific states. Volume II. Stanford, California. Stanford University Press. 635.
Anonymous. 2008a. Vascular plants, bryophytes, and lichens list. California Department of Fish and Game, Natural Diversity Database, Sacramento. Quarterly Publication. 70p.
Anonymous. 2008b. California Natural Diversity Data Base. RareFind.Version 3.1.1. Sacramento. California Department of Fish and Game.
Hoover, R.F. 1970. The vascular plants of San Luis Obispo County, California. Berkeley. University of California Press. 350.
Mason, H.L. 1957. A flora of the marshes of California. Berkeley. University of California Press. 868.
Rollins, R.C. 1993. The Cruciferae of continental North America. Stanford, California. Stanford University Press. 976.