43. Nasturtium W. T. Aiton in W. Aiton and W. T. Aiton, Hortus Kew. 4: 110. 1812.
Watercress [Latin nasus, nose, and tortus, distortion, alluding to pungency of plants]
Ihsan A. Al-Shehbaz
Perennials; (aquatic, rhizomatous, rooting at proximal nodes); not scapose; often glabrous, sometimes pubescent. Stems prostrate or decumbent, or erect in emergent plants, unbranched. Leaves cauline; not rosulate; petiolate; petiole base sometimes auriculate, blade (pinnately compound in emerged plants, or simple in deeply submerged plants, lateral leaflets petiolulate or sessile, 1-6(-12) pairs), margins entire, repand, or, rarely, dentate. Racemes (corymbose, several-flowered), elongated in fruit. Fruiting pedicels divaricate or descending, slender, (glabrous or adaxially puberulent). Flowers: sepals erect or ascending, oblong [ovate], lateral pair subsaccate or not saccate basally, (glabrous); petals usually white, rarely pink, obovate or narrowly spatulate, (longer than sepals), claw undifferentiated from blade, (attenuate to clawlike base, apex obtuse, acute, or rounded); stamens tetradynamous; filaments (white), not dilated basally; anthers oblong, (apex obtuse); nectar glands (2), lateral, annular or semiannular. Fruits siliques, sessile, usually linear, rarely narrowly oblong, smooth or slightly torulose, straight or slightly curved, terete; valves each obscurely veined, glabrous; replum rounded; septum complete; ovules 25-50 per ovary; style obsolete or distinct; stigma capitate. Seeds plump, not winged, oblong or ovoid; seed coat (minutely to coarsely reticulate), not mucilaginous when wetted; cotyledons accumbent. x = 8.
Species 5 (4 in the flora): North America, n Mexico, Central America, Europe, Asia, n Africa; introduced also in South America, tropical and s Africa, Australia, nearly worldwide.
SELECTED REFERENCES Al-Shehbaz, I. A. and R. A. Price. 1998. Delimitation of the genus Nasturtium (Brassicaceae). Novon 8: 124-126. Al-Shehbaz, I. A. and R. C. Rollins. 1988. A reconsideration of Cardamine curvisiliqua and C. gambellii as species of Rorippa (Cruciferae). J. Arnold Arbor. 69: 65-71. Green, P. S. 1962. Watercress in the New World. Rhodora 64: 32-43. Rollins, R. C. 1978. Watercress in Florida. Rhodora 80: 147-153.