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Rorippa sessiliflora (Nutt.) Hitchc.
Family: Brassicaceae
stalkless yellowcress,  more...
Rorippa sessiliflora image
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.

Annual herb 20 - 40 cm tall Stem: normally upright, normally branched. Flowers: in branched clusters (racemes). Sepals four, strongly sac-shaped. Petals none. Stamens three to six. Fruit: a thick pod (silique), spreading or ascending, 7 - 10 mm long, often over 2 mm wide. Seeds numerous. Lower leaves: alternate, often pinnately divided below the middle, stalked, oblong- reverse lance-shaped, coarsely toothed. Upper leaves: alternate, stalked, progressively smaller, reverse lance-shaped to egg-shaped, sometimes round-toothed.

Similar species: No information at this time.

Flowering: late May to early August

Habitat and ecology: Occasional in muddy or sandy ground along ponds, rivers, and streams. Also found in other moist areas.

Occurence in the Chicago region: native

Etymology: Rorippa possibly comes from the Latin roro, meaning "to be moist," and ripa, meaning riverbank. Sessiliflora means "with stalkless flowers."

Author: The Morton Arboretum

Glabrous annual 2-4 dm, normally erect and branched; lower lvs oblong-oblanceolate, coarsely crenate and often ±pinnatifid below the middle, the upper progressively smaller, petiolate, oblanceolate to ovate, entire to crenate; sep strongly saccate; pet wanting; stamens 3-6; mature pedicels widely divergent, 0.5-2 mm; frs spreading or ascending, thick (often over 2 mm), often slightly falcate, 7-10 mm, with numerous (commonly 150-200) seeds, these tiny (to 0.5 mm), deeply pitted, appearing rough at 10׻ style to 0.4 mm, or none; 2n=16. Wet soil and shallow water; Fla. to Tex., n. to D.C., O., Ind., s. Minn., and Neb. May-Oct. (Radicula s.)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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