Cardamine hirsuta is an annual, winter annual herb, stem 10-40 cm tall, smooth. Name hirsuta is rather misleading since this plant looks hairless without a lens. Even then, hairs are sparse.
Leaves alternate, mostly in a dense basal rosette, pinnate, leaflets rounded, short-stalked, terminal leaflet larger, often lobed, stem leaves few, inconspicuous, becoming narrower towards top of stem, leaf stalks hairy, at least at base (use lens).
Flowers white, 4-parted, petals 0.2-0.3 cm long, sepals green, shorter; inflorescence crowded at top of a gradually elongating stem with a few small pinnate leaves; blooming March-April.
Fruit green, often purplish, eventually becoming dry, capsules linear, to 2.5 cm long, developing below flowers on the elongating stem. the uppermost fruit often longer than the inflorescence; .
Wetland status: FACU.
Frequency in NYC: Very infrequent.
Habitat: Lawns, gardens, weedy areas, open moist soil.
Notes: Very common agricultural, nursery, and garden weed outside NYC, often forming mats of seedlings and small plants (Altland 2006).