Cardamine corymbosa aka New Zealand Bitter Cress

Cardamine corymbosa is known as New Zealand bittercress. It belongs to the mustard family, Brassicaceae. Its native range includes New Zealand and Macquarie Island. It has spread to Australia, North America, Britain, and western Europe. It grows beside streams, along paths, and in disturbed ground. It also occurs in forests, at woodland edges, and in cultivated areas. Plants can settle into cracks and narrow rock ledges.

This small herb grows close to the ground. NCSU describes it as perennial, while Kew lists it as annual. Plants reach about 0.25–0.5 feet [0.08–0.15 metres] tall. Their spread reaches 0.5–1 foot [0.15–0.30 metres]. The plant has a fine texture and thin, wiry growth. It creeps outward and forms new plants at its nodes. Bright green leaves form a flat basal rosette or short side branches. Each leaf usually has one egg-shaped leaflet on a long petiole. Some have two smaller leaflets beneath the main one. Leaf surfaces range from smooth to sparsely hairy. Their edges lack teeth, and each leaf measures under an inch.

Small white flowers appear from early spring through fall. Each flower has four petals in a cross shape. The flower clusters take the form of a corymb. Straight green flower stems reach about 0.17–0.25 feet [0.05–0.08 metres]. Pods can begin forming before the flower sheds its petals. Each smooth pod is a siliqua, less than an inch long. Green pods turn purplish brown as they ripen. They then split open and scatter their tiny seeds. The seeds range from pale green to yellowish brown.

This species grows in full sun or partial shade. It accepts clay, loam, sand, and shallow rocky ground. It grows in moist soil and tolerates some flooding. It also copes with sites that dry out at times. Kew places it in a temperate climate. The supplied sources give no numbered hardiness rating.

Its main garden role is as a weed, not an ornamental. Growth is fast, and plants can flower within weeks. Nursery stock has carried it between sites. NCSU advises prompt removal to limit its spread. Hand weeding and stopping flowering help control it. NCSU reports no major pest or disease problems. The supplied evidence does not establish food uses or toxicity.