Rorippa aquatica
Rorippa crystallina
lake yellow-cress, lakecress
Mackenzie River yellowcress
erect, unbranched or often branched distally, 3–8.5(–11) dm.
(simple from base), erect, branched distally, 1–4 dm.
absent.
rosulate;
[petiole (1.5–)3–7.7(–12) cm];
blade [(2.5–)4–14(–22) cm × (10–)20–40(–70) mm], margins dentate to crenate.
submerged shortly petiolate, emergent sessile or petiolate (to 2 mm);
blade: submerged pectinate, finely 1–4-pinnatisect into filiform or capillary segments, emergent lanceolate to oblong, usually undivided, rarely lobed, (1.5–)2–5.5(–6.7) cm × (5–)7–15(–20) mm, margins entire or dentate.
petiolate or subsessile;
blade ovate to lanceolate, 2.5–7 cm × 4–13 mm (smaller distally), base cuneate, not auriculate, margins dentate.
elongated.
elongated.
sepals (deciduous after anthesis), ascending, oblong, 2–4 × 1.4–1.8 mm;
petals white, spatulate to obovate, 4–8 × 2–3.5 mm;
median filaments 3–4 mm;
anthers linear, 1.7–2.2 mm.
sepals (deciduous after anthesis), erect, oblong, 4–5 × 1–1.5 mm;
petals whitish, oblanceolate, 6–8 × 2.5–3 mm;
median filaments 3–4.2 mm;
anthers oblong, 0.8–1.2 mm.
divaricate to horizontal or slightly reflexed, straight or curved, (5–)7–15 mm.
divaricate to horizontal, straight, 12–20(–26) mm.
silicles, straight, oblong to ellipsoid, 4–7 × 2.5–3 mm; (septum reduced to a rim);
ovules 48–80 per ovary;
style 2–4 mm; (stigma slightly 2-lobed).
siliques, straight or slightly curved, linear, 14–26 × 2–2.8 mm;
ovules 28–40 per ovary;
style 0.3–1 mm.
biseriate, brown to reddish, ovoid, 0.7–0.8 mm (0.5–0.6 mm diam.), reticulate.
uniseriate, brown, ovoid, 1.6–2 mm (1.2–1.5 mm diam.), colliculate.
= 24.
= 32.
Rorippa aquatica
Rorippa crystallina
Submerged leaves of Rorippa aquatica often detach readily and produce adventitious buds from which new plantlets develop. The infrequent production of seeds in this species may indicate that it is self-incompatible and that most or all plants within a given population might be the result of asexual reproduction. It appears to prefer slow, unpolluted, running water. The apparent wide distribution does not reflect how uncommon the species is in any given area. Based on the relatively small number of recent collections in major herbaria, it is likely that most of the county records given by I. A. Al-Shehbaz and V. M. Bates (1987) reflect populations that have disappeared.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
In his original description of Rorippa crystallina, Rollins considered the presence of calcium oxalate crystals in the plant to be a unique feature, but this was later found to be an artifact of treating the plants with formaldehyde (R. L. Stuckey 1972; R. C. Rollins 1993). Characterization of the species as native to Canada was questioned by G. A. Mulligan and W. L. Cody (1995), who believed that it was probably introduced from China. There is no species of mustard from elsewhere in the world that closely resembles R. crystallina, and it should be considered a Canadian endemic.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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