Rorippa sessiliflora (Nutt.) Hitchc.
CC = 3
CW = -5
MOC = 53
Family - Brassicaceae
Habit - Taprooted annual forb.
Stems - Ascending to erect, to 50 cm, not rooting at the nodes or rooting sporadically only at the lowermost few nodes, branching in the upper half, ridged, glabrous.
Leaves - Basal and alternate, 1.5-10.0 cm long, glabrous, the basal and lowermost stem leaves petiolate, the base not or only slightly clasping the stem, simple and entire or wavy-margined to pinnately lobed with 3-15 blunt, irregular lobes, the lobes linear to irregularly ovate, the margins entire, wavy, or with few, shallow, blunt teeth. Leaves becoming less divided and smaller upward.
Inflorescence - Terminal and axillary racemes, compact in flower, quickly elongating in fruit to 15 cm. Rachis of the inflorescence glabrous. Pedicels of the flowers 0-1 mm long, to 2 mm long in fruit, typically spreading perpendicular to the stem in fruit.
Flowers - Sepals 4, 1-2 mm long, pale yellow, erect, glabrous, rounded at the apex, slightly inflated. Petals absent or very minute, when present the petals are spatulate, 2 mm long, .5 mm broad, glabrous, translucent yellow, fugacious. Stamens 4, erect. Filaments glabrous, 2.0-2.2 mm long, translucent white. Anthers yellow. Ovary green, glabrous, 1-2 mm long in flower, cylindrical, quickly expanding. Style absent or less than 0.5 mm. Stigma capitate, 0.8 mm broad.
Fruits - Siliques 5-10 mm long, 1.8-3.0 mm wide, oblong, straight or slightly arched upward, the surface glabrous, smooth or slightly roughened with minute, light-colored ridges, the stalk up to 2.5 mm long. Seeds mostly 100-200 per fruit, in 2 rows in each locule, 0.4-0.5 mm long, circular or somewhat cordate in outline, the surface with a fine, netlike or honeycomb-like pattern of ridges and pits, tan to light yellowish brown.
Flowering - April - October.
Habitat - Bottomland forests, streambanks, sloughs, levees, railroads, and roadsides.
Origin - Native to the U.S.
Lookalikes - Other species of Rorippa.
Other info. - This species can be found in nearly every county bordering the large rivers, as well as scattered through other regions of Missouri. It is absent from much of the central Ozarks, which Yatskievych speculated might be due to the lack of muddy habitats in this region. The plant can be identified by its habitat, divided lower leaves, minute flowers, and many-seeded fruits. The flowers usually lack petals. The short pedicels of the fruit are the shortest of any Rorippa species in the state.
Photographs taken at Davis Ferry, Monroe County, AL., 3-26-06 (DETenaglia); also at Columbia Bottoms Conservation Area, St. Charles County, MO, 4-24-2016 (SRTurner).