Rorippa sylvestris (L.) Besser
Creeping Yellow Cress
CC = *
CW = -3
MOC = 25
Family - Brassicaceae
Habit - Rhizomatous perennial forb.
Stems - Ascending to erect, to 80 cm, rarely rooting at the lowermost nodes, glabrous or nearly so.
Herbaceous, erect, from rhizomes, glabrous, green or becoming purple in the strong sun, ribbed, to +/-35cm tall, branching.
Leaves - Leaves basal and alternate, 3.5-15.0 cm long, petiolate, the bases not clasping the stem, pinnately lobed or divided, with 5-13 lobes or divisions, these linear to oblong or irregularly obovate to ovate, the margins with several sharp teeth, glabrous.
Inflorescence - Terminal and axillary racemes. Pedicels to 4 mm in flower, expanding to 1 cm in fruit, glabrous. Inflorescence compact in flower, quickly elongating. Siliques to 1cm long, 1mm in diameter, cylindric but slightly compressed, glabrous, with a beak to 1mm long.
Flowers - Sepals 4, 2-4 mm long, yellow, erect to spreading. Petals 4, 4-6 mm long, distinct, spatulate, yellow, glabrous, rounded at the apex. Stamens 6, erect, 4 larger and 2 smaller. Filaments yellow, glabrous, to 3 mm long. Anthers yellow, 1 mm long. Styles 0.5-1.0 mm long, the stigma capitate and wider than the style. Ovary cylindric, green-yellow, glabrous, 2 mm long in flower, superior.
Fruits - Siliques 10-20 mm long, 1-2 mm wide, linear, often slightly arched upward. Seeds produced uncommonly, mostly 25-80 per fruit, in 2 rows in each locule, 0.6-0.7 mm long, oblong in outline, the surface faintly and finely bumpy, reddish brown.
Flowering - May - September.
Habitat - Bottomland forests, sloughs, crop field margins, pastures, ditches, railroads, roadsides, open moist disturbed areas.
Origin - Native to Europe.
Lookalikes - Other species of Rorippa.
Other info. - This little species can be found scattered locations in Missouri, mostly in counties bordering the big rivers. Its distribution in the U.S. is likewise scattered, and predominantly in the Northeast. The plant is recognized by its leaves which are pinnately divided with toothed leaflets, and yellow, mustard-patterned flowers. Differentiation from other members of the genus can be difficult, but in general this species has flowers with relatively large petals, and leaves with sharply toothed leaflets and bases which do not clasp the stem. The plant is found only in moist areas.
Photographs taken near Columbia, MO., 5-29-04 (DETenaglia); also at Riverfront Park, Washington, Franklin County, MO, 5-25-2012 and 5-13-2018 (SRTurner).