Creeping Yellowcress

In Great Britain and/or Ireland:
Foodplant / parasite
colony of sporangium of Peronospora parasitica parasitises live Rorippa sylvestris
Remarks: season: 1-4

Foodplant / open feeder
larva of Phaedon cochleariae grazes on live leaf of Rorippa sylvestris
Remarks: season: -early 9

It seems to be rare in our area, but distinct by its bright yellow flowers with conspicuous petals and much dissected leaves. Leaves may confuse with some Cardamine species but yellow flowers are distinctive.

Although the present authors have not examined the type of Rorippa liaotungensis, the detailed description and illustration leave no doubt that it is a synonym of R. sylvestris, hundreds of specimens of which were examined from its native and naturalized ranges.

Perennial, stoloniferous, 20-50 cm tall, suberect or procumbent with ascending branches, ± glabrous. Leaves pinnate or deeply pinnatisect, lower stalked, upper subsessile or sessile; lobes obovate to oblong, cuneate, sinuate-toothed to subentire, apex rounded. Racemes (20-) 30-60-flowered, up to 15 cm long in fruit. Flowers 4-5 mm across, yellow; pedicels up to 10 (-12) mm long in fruit, spreading. Sepals c. 2.5 mm long. Petals 4-5 mm long, 1.5-2 mm broad. Stamens c. 2:3 mm long. Siliquae 9-18 mm long, 1.5-2 (-2.5) mm broad, linear-oblong, cylindrical, glabrous; style c. 1 mm long with capitate stigma; seeds many, ± biseriate, c. 0.7 mm long.

Herbs perennial, (5-)15-80(-100) cm tall, glabrous or sparsely pubescent. Stems prostrate, decumbent, ascending, or suberect, branched mainly basally. Rosette leaves soon withered, similar to cauline leaves. Middle cauline leaves petiolate, deeply pinnatisect; petiole not auriculate, rarely minutely auriculate; leaf blade (2-)3.5-15(-20) × (0.7-)1-4.5(-6) cm; lateral lobes 3-6 on each side of midvein, sublinear, lanceolate, oblong, elliptic, or ovate, margin dentate or serrate, sometimes subentire; uppermost leaves with 1-3 lateral lobes or not lobed, often subsessile. Racemes ebracteate. Fruiting pedicels (3-)4-10(-12) mm, slender, divaricate. Sepals green or yellow, oblong, 1.8-3(-3.5) × 0.7-1.5 mm, ascending or spreading. Petals yellow, spatulate or obovate, (2.2-)2.8-5.5(-6) × 1.5-2.5 mm, apex rounded. Filaments (1.5-)1.8-3.5(-4) mm; anthers oblong, 0.7-1 mm. Ovule number highly variable, mostly aborted. Fruit linear, very rarely oblong-linear, (0.4-)0.7-2(-2.5) cm × (0.7-)1-1.3(-1.6) mm, rarely producing seeds; style 0.5-1(-1.5) mm; stigma subentire or slightly 2-lobed. Seeds reddish brown, ovoid, colliculate, uniseriate or rarely subbiseriate, 0.6-0.9 × 0.4-0.5 mm. Fl. and fr. May-Sep. 2n = 32, 40, 48.

Distribution: Temperate Eurasia.

Xinjiang, Liaoning [India, Japan, Kashmir, Russia, Tajikistan, Uzbekistan; SW Asia, Europe; introduced in North and South America].

Fl. Per.: May-August.

Along ditches, damp areas, meadows, waste grounds, fields; 100-2000 m.

Sisymbrium sylvestre Linnaeus, Sp. Pl. 2: 657. 1753; Nasturtium sylvestre (Linnaeus) R. Brown; Rorippa liaotungensis X. D. Cui & Y. L. Chang.

Rorippa sylvestris (the creeping yellowcress, keek, or yellow fieldcress; syn. Radicula sylvestris (L.) Druce ) is an invasive species of plant in the United States, likely entering from Europe before 1818 from ballast water and spreading throughout North America through contaminated nursery seed stock.