Creeping Yellow-cress

Native to Europe and Asia and now widely established throughout North America, Rorippa sylvestris can be confused with the native annual Bog Yellow-cress (Rorippa palutris). Creeping Yellow-cress however is a perennial, forming dense colonies, its flowers are over twice the size of R. palustris, and its mature fruit longer and more slender. All three of our own observations and 1 of 6 herbarium records were from nursery production fields - a high risk pathway for this pesky weed.

Flower: 
 Elongating clusters of stalked flowers at the end of branching stems. The yellow flowers are ¼ inch across, forming at the tip of the expanding raceme, the 4 petals rounded, spatula shaped, twice as long as the sepals, the narrowed base of the petals creating a wide gap between them. Typically two racemes branch off at the tip of the stem

Leaves and stems:
Young plants form basal rosettes from underground stems. Lower leaves are oblong in outline, up to 8 inches long and ¾ inch wide, with a compound look to them, deeply divided into lobes that also have lobed or coarsely toothed edges. Upper leaves are somewhat smaller. Stems are creeping, forming dense colonies, with ascending branches, glossy or with few sparse hairs lower down.

Fruit:
Fruit is a slender green pod up to ½ inch long, angled out and somewhat up from the stalk.