Nasturtium sessiliflorum Nuttall in J. Torrey and A. Gray, Fl. N. Amer. 1: 73. 1838; N. limosum Nuttall; Radicula limosa (Nuttall) Greene; R. sessiliflora (Nuttall) Greene

Annuals; glabrous throughout. Stems (simple or several-branched from base) erect, branched distally, (0.9-) 2-4.5(-6.3) dm. Basal leaves not rosulate; blade margins dentate. Cauline leaves shortly petiolate or sessile; blade oblong or oblanceolate to obovate, 1.5-7(-13.3) cm × (5-)10-28(-50) mm, (lateral lobes much smaller than terminal), base auriculate or not, margins dentate or less frequently sinuate, or (lateral lobes) denticulate or entire. Racemes considerably elongated. Fruiting pedicels divaricate-ascending to horizontal, straight, 0.5-2(-4) mm, (slender or stout). Flowers: sepals ascending to spreading, ovate, 1.2-2 × 0.5-0.8 mm; petals absent; median filaments 1-1.6 mm; anthers ovate, 0.2-0.3 mm. Fruits siliques, straight or curved, oblong to oblong-linear, (4-)6-9(-12) × (1.4-)1.8-2.8(-3.5) mm; ovules 158-242 per ovary; style 0.1-0.5 mm. Seeds biseriate, yellow-brown, cordiform, 0.4-0.5 mm, foveolate. 2n = 16.

Flowering Mar-Oct. Mud flats, ditches, wet old fields, roadsides, sloughs, fallow fields, floodplains, stream banks, edges of pools, waste grounds, gardens; 0-300 m; Ala., Ark., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Mass., Miss., Mo., Nebr., N.C., Ohio, Okla., S.C., S.Dak., Tenn., Tex., Va., Wis.

Both R. L. Stuckey (1972) and R. C. Rollins (1993) indicated that Rorippa sessiliflora has strongly saccate sepals, but all specimens that I examined failed to show any sign of this character. The species is very distinctive and can easily be distinguished by an absence of petals and by having fruiting pedicels 0.5-2(-4) mm.