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 3 to 5 mm long, rounded, spatula shaped, twice as long as the sepals, the narrowed base of the petals creating a wide gap between them.

Leaves and stems:

Young plants form basal rosettes that disappear after the first year. Basal and lower stem leaves are oblong in outline, up to 8 inches (to 20 cm) long and ¾ inch wide, deeply divided into lobes that may be further lobed or have coarsely toothed edges. Leaves are hairless and become smaller and the divisions narrower as they ascend the stem. Stems are erect to ascending to prostrate, usually branched, ribbed, hairless or with sparse hairs on the lower stem. Plants can form dense colonies from creeping, underground stems (rhizomes).

Fruit:

Fruit is a slender green pod up to ½ inch (10 to 15 mm) long, mostly straight, angled out and somewhat up from the stalk.

Notes:

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 weed.