Cardamine rotundifolia aka American Bittercress

Cardamine rotundifolia is a perennial in the mustard family, Brassicaceae. Its common names include American mountain watercress and round-leaved cuckoo flower. It comes from eastern North America, but not Britain or Ireland. Its native range includes New York, Ohio, Missouri, North Carolina and Kentucky. In the wild, it grows beside cold springs and brooks. These damp sites help explain its need for steady moisture.

This low plant reaches about 1 foot [0.3 metres] tall. Its spread reaches about 1.6 feet [0.5 metres]. It forms mats as stolons spread across the ground. This growth form suits low planting beside water or in bog gardens. It flowers from April through August, and seeds ripen from May through September. Each flower has both male and female organs. Bees, flies, moths and butterflies pollinate the flowers. The plant can also set seed with its own pollen.

Give it moist, humus-rich soil in shade or partial shade. It can also grow in full sun, according to Plants For A Future. The soil must not dry out. It accepts sandy, loamy and clay soils, so texture need not limit planting. It also tolerates mildly acid, neutral and mildly alkaline ground. Wet soil and shallow water suit it, as well as moist ground. Plants For A Future lists USDA hardiness zones 5–9. Its need for wet ground makes it a choice for pond edges.

The leaves are edible, either uncooked or cooked. They have a sharp taste like watercress. Plants For A Future gives its food value two out of five. The same source reports no known hazards. That report does not establish safety for every person or pet. It lists no known medicinal uses or other uses. It also does not flag the plant as a weed.

Raise new plants from seed sown in a cold frame in spring. At 59°F [15°C], seeds generally sprout within one to three weeks. Move seedlings into separate pots once they are large enough. Keep young plants in light shade under cover for their first two years. Division offers another way to increase a clump. Divide in early spring or after summer dieback. Replant large divisions straight into their final sites. Grow small divisions in pots until they root well.