Rorippa sylvestris (L.) Bess.
Creeping Yellow Cress
Family - Brassicaceae
Stems - Herbaceous, erect, from rhizomes, glabrous, green or becoming purple in the strong sun, ribbed, to +/-35cm tall, branching.
Leaves - Alternate, petiolate, deeply pinnatifid. Basal leaves to -10cm long, 2-2.5cm broad, with +/-6 main divisions per side. Cauline leaves similar but reduced. All leaves glabrous or with very few short hairs. Divisions of the leaves toothed. Upper leaves with thinner and fewer divisions than the lower. Tissue connecting the divisions of the leaves .2-.3mm broad (use a lens to see).
Inflorescence - Terminal and axillary racemes to +10cm long. Axis glabrous. Pedicels to 4mm long in flower, expanding to +/-1cm long in fruit, glabrous. Inflorescence compact in flower, quickly expanding. Siliques to 1cm long, 1mm in diameter, cylindric but slightly compressed, glabrous, with a beak to 1mm long.
Flowers - Petals 4, distinct, spatulate, yellow, glabrous, to +4mm long, 1.5mm broad, rounded at the apex. Stamens 6, erect, 4 larger and 2 smaller. Filaments yellow, glabrous, to 3mm long. Anthers yellow, 1mm long. Ovary cylindric, green-yellow, glabrous, 2mm long in flower, superior. Style .5mm long. Stigmas globose-capitate, .7mm broad. Sepals 4, distinct, yellow, erect to spreading, cupped, mostly glabrous but often with a few hairs at the apex externally, entire, 2-2.5mm long, to 1mm broad, subulate.
Flowering - May - September.
Habitat - Moist low ground, streambanks, wet fields and meadows.
Origin - Native to Europe.
Other info. - This little species can be found scattered throughout Missouri. The plant can be identified by its yellow flower petals, which are 4-8mm long, and its pinnately divided leaves, which have toothed margins. The wet habitat of the plant and its creeping stems with fibrous roots are other good characteristics to look for.
Photographs taken near Columbia, MO., 5-29-04.