Cardamine lacustris (Garn.-Jones & P.N.Johnson) Heenan

Annual rosette herb; stems on young plants very short, on older plants lateral, ascending at first, later prostrate, geniculate, rooting regularly, up to 50 mm long, reaching 0.8–2.0 mm diam., glabrous or sometimes with sparse, fine, slightly recurved hairs. Leaves glabrous, or with sparse, simple hairs on petiole, slightly glossy, dull green or tinged purplish grey, in rosettes and clustered on stems; early rosette leaves entire, linear-spathulate; later rosette and cauline leaves pinnatifid, 20–50 mm long; petiole 2.0–12.0 mm long, 0.5–1.0 mm wide; terminal lobe narrow-spathulate, 2.0–5.0 mm broad; lateral lobes narrowly oblong-spathulate, 4.0–10.0 mm long, sometimes single or in uneven numbers, but usually in 1–3 subopposite pairs. Inflorescence short-racemose, 1.0–2.0 mm long, reaching 2.0–5.0 mm long at fruiting; peduncle glabrous. Sepals suberect, oblong, glabrous, green with narrow, pale margins, 1.5–2.0 × 0.6–1.0 mm. Petals white, suberect, oblong- to obovate-spathulate, obtuse, 1.8–2.5 × 0.8–1.2 mm, weakly clawed; limb spreading. Stamens suberect; median stamens usually 2, rarely 4, 1.6–2.0 mm long; lateral stamens 1.0–1.5 mm long. Ovary ellipsoid, 1.0–1.6 mm long; stigma sessile, 0.4 mm diam.; locules each with 5–8 ovules. Silicle elliptic to oblong, 1.0–3.5 × 1.0–1.7 mm; valves pale straw-coloured, thin, convex, glabrous, not veined or with 1 weak vein. Seeds 0.6–0.9 mm long, 0.3–0.4 mm wide, 0.2–0.25 mm thick, oblong, yellow-brown to henna; wing absent.

The plants typically grow on cobble beaches on lake shores and tarn margins, in silty sediments lodged between stones.

Flowering January–February; Fruiting February–March.

Chromosome number 2n = 48.