Nasturtium, which is often reduced to synonymy of Rorippa, is recognized as a distinct genus of five species. It is more closely related to Cardamine than to Rorippa, and its distinguishing characters from these genera are given. The new combination N. floridanum is proposed, and a key to the species is provided. The generic status and limits of Nasturtium R. Brown have been the subject of considerable controversy. In some of the recent accounts (e.g., Czerepanov, 1995; Hedge, 1968; Jonsell, 1993; Mabberley, 1997; Stuckey, 1972; Wannenmacher, 1986) the genus has been maintained, whereas in others (e.g., Al-Shehbaz, 1988; Al-Shehbaz & Rollins, 1988; Green, 1962; Jonsell, 1988; Rich, 1991; Rollins, 1993) it is reduced to synonymy of Rorippa Scopoli. Schulz (1936) also united the two genera, but he adopted Nasturtium for the combined genus, instead of the earlier-published Rorippa. The basic disagreement among these treatments is whether or not the morphological differences between Nasturtium and Rorippa are sufficient to clearly distinguish the genera. There are numerous other examples of generic pairs in the Brassicaceae with similar controversial boundaries. Because of convergence in almost every conceivable character, emphasis on a small number of morphological characters can often result in artificial generic groupings within the family. The use of molecular data, along with critical evaluation of morphology, can often help resolve conflicts between competing hypotheses about the limits and relationships of genera of the Brassicaceae (Al-Shehbaz & Warwick, 1997; O'Kane & Al-Shehbaz, 1997). A case in point is the delimitation of Nasturtium and Rorippa. Sequence comparisons of chloroplast DNA consistently support the separation of Nasturtium as a genus very distinct from Rorippa, and indicate that Nasturtium is most closely related to the cosmopolitan genus Cardamine L. This result was obtained by Les (1994), who compared sequences of the gene rbcL for six species in the cardaminoid group of Brassicaceae and found relatively strong support for a grouping of N. officinale R. Brown with C. pensylvanica Muhlenberg ex Willdenow, while two species of Rorippa, R. sylvestris (L.) Besser (the generic type) and R. amphibia (L.) Besser, formed a separate clade more closely related to lakecress (Neobeckia aquatica (Eaton) E. L. Greene) and horseradish (Armoracia rusticana P. Gaertner). Recent comparisons of the more rapidly changing chloroplast gene ndhF and the trnL-F intron and spacer regions (Price & Sweeney, in prep.) indicate that the endangered species N. gambellii (S. Watson) 0. E. Schulz forms a well supported clade with N. officinale and that the genus Nasturtium is much more closely related to Cardamine than to other genera in the cardaminoid group, including Armoracia Gaertner et al., Rorippa, and Barbarea R. Brown. As presently delimited, Nasturtium is readily distinguished from Rorippa by a combination of characters, including a perennial, almost always aquatic habit, hollow stems rooting at the submersed and lower nodes, pinnate emergent leaves with 1-9(-15) pairs of lateral leaflets that are never decurrent on the rachis, white flowers, curved, cylindric fruits, and reticulate seed coats, and by the absence of median nectar glands. Species of Rorippa are annuals or perennials of wet or mesic areas and almost always have taproots and only very rarely (e.g., R. amphibia and R. fluvitalis (E. Meyer ex Sonder) Thellung, both of which are yellow-flowered aquatics with simple leaves) root at the lowermost nodes. They have solid or rarely hollow stems, yellow or occasionally white flowers, nearly always median nectar glands, and colliculate, minutely rugose, papillose, verrucose, or reticulate seeds. The leaves of Rorippa range from entire to toothed, sinuate, or pinnatisect, and rarely form leafletlike lobes. When leafletlike lobes are present, they are always decurrent on the rachis, and the uppermost leaves are often simple. Nasturtium plants growing in water almost always produce simple leaves on submersed stems, but emergent NovoN 8: 124-126. 1998. This content downloaded from 157.55.39.161 on Mon, 23 May 2016 06:19:21 UTC All use subject to http://about.jstor.org/terms Volume 8, Number 2 1998 Al-Shehbaz & Price Delimitation of Nasturtium 125 shoots always produce compound leaves (Michaelis, 1976; Rollins, 1978). The fruits of Rorippa range from globose to ovoid, oblong, clavate, or cylindric. Cardamine is readily distinguished from Nasturtium by its unique fruits that dehisce explosively, by its spirally coiled valves that lack a distinct midvein, and by its flattened replum. In Nasturtium the fruits do not dehisce explosively, the valves have a distinct midvein and do not coil after dehiscence, and the replum is rounded. Nasturtium as circumscribed here includes five species: N. officinale (the type species, which is the watercress of commerce) and N. microphyllum Boenninghausen ex Reichenbach (both of which are native to Eurasia and northern Africa and widely naturalized elsewhere), the Moroccan N. africanum Braun-Blanquet, and the North American N. gambellii (California, Mexico), and N. floridanum (Al-Shehbaz & Rollins) Al-Shehbaz & Price (Florida). A new combination for the last is herein proposed. Nasturtium valdes-bermejoi Castroviejo, which was described from Spain (Castroviejo, 1986), appears to be a minor variant of N. microphyllum. It was not recognized in the revised account of the genus for Flora Europaea (Valentine, 1993), and its alleged differences from N. microphyllum clearly fall within the variation range of that species. Further study is needed of several morphologically anomalous species that appear to fit better into Rorippa than into Nasturtium. The recently discovered New Caledonian Rorippa neocaledonica Jonsell (Jonsell, 1995, 1997) is an annual with decurrent leafletlike lobes, yellow flowers, and verruculose seeds, and it does not produce adventitious roots at the lower nodes. We have not seen the type or other material of the species, and we believe that the species is a good member of Rorippa. It appears to be related to R. sarmentosa (DC.) J. F. Macbride of the Pacific Islands (Jonsell, 1997; Smith, 1981; Wagner et al., 1990). Though R. sarmentosa has compound leaves and is sometimes perennial with adventitious roots at the lower nodes, it clearly differs from Nasturtium in being a mesic rather than aquatic plant, and in having solid stems, median nectaries, yellow flowers, and papillose seeds (Jonsell, 1997). The Madagascar endemic R. laurentii Jonsell (Jonsell, 1979) has white flowers and pinnatisect leaves, but its erect stems that do not root at the lower nodes, broadly flattened fruits, median nectar glands, and ridged seeds clearly exclude it from Nasturtium. Key to the Species of Nasturtium la. Seeds biseriate in each locule, coarsely reticulate, with 25-50(-60) areolae on each side; mature fruit (1.8-)2-3 mm wide ...... .N. officinale lb. Seeds uniseriate in each locule, moderately to minutely reticulate, with more than 100 areolae on each side; mature fruit 0.8-1.2(-1.8) mm wide. 2a. Emergent leaves not auriculate at base, 3or very rarely 5-foliolate; seeds yellowish brown; style obsolete; plants endemic to Florida .N. floridanum 2b. Emergent leaves often minutely auriculate at the petiole base, (3 or)5-15-foliolate; seeds reddish brown; style distinct; plants of other parts of the world. 3a. Fruit abruptly ending in a style to 1 mm; leaflets entire to repand; seeds with 100-150(-175) areolae on each side . N. microphyllum 3b. Fruit attenuate into a slender style 1.52.5 mm; leaflets often coarsely dentate, rarely subsinuate-repand; seeds with 300-450 areolae on each side. 4a. Fruits 0.8-1(-1.5) mm wide; seeds not mucilaginous when wetted; plants of California and Mexico . . N. gambellii 4b. Fruits 1.5-1.8 mm wide; seeds mucilaginous when wetted; plants of Morocco N. africanum Nasturtium floridanum (Al-Shehbaz & Rollins) Al-Shehbaz & Price, comb. nov. Basionym: Rorippa floridana Al-Shehbaz & Rollins, J. Arnold Arbor. 69: 68. 1988. Cardamine curvisiliqua Shuttleworth ex Chapman, Fl. South. U.S. 605. 1887; not Rorippa curvisiliqua (W. J. Hooker) Bessey ex Britton, Mem. Torrey Bot. Club 5: 169. 1894; not Nasturtium curvisiliquum (W. J. Hooker) Nuttall ex Torrey & A. Gray, Fl. N. Amer. 1: 73. 1838. Nasturtium stylosum Shuttleworth ex O. E. Schulz, in Engler & Prantl, Nat. Pflanzenfam., ed. 2, 17B: 553. 1936; not N. stylosum (DC.) O. E. Schulz ex Cheesman, Trans. & Proc. New Zealand Inst. 43: 179. 1911; not Rorippa stylosa (DC.) Allan, Fl. New Zealand 1: 188. 1961; not R. stylosa (Persoon) Mansfield & Rothmaler, Repert. Spec. Nov. Regni Veg. 49: 276. 1940. TYPE: U.S.A. Florida: "in uliginosis subsalsis ad fluv. St. Marks, prope St. Marks, April-May 1843," Rugel s.n. (lectotype, designated by AlShehbaz & Rollins (1988); isolectotype, GH). Rorippa floridana was proposed by Al-Shehbaz and Rollins (1988) as a new name for the Florida endemic Cardamine curvisiliqua Shuttleworth ex Chapman, because the transfer of the latter name to Rorippa would have created a later homonym of R. curvisiliqua (W. J. Hooker) Bessey ex Britton, a This content downloaded from 157.55.39.161 on Mon, 23 May 2016 06:19:21 UTC All use subject to http://about.jstor.org/terms