Agalinis purpurea is an annual herb to 120 cm tall; a root hemiparasite; stems simple to branched, 4-sided, smooth.
Leaves opposite (often alternate on branches), largest leaves to 0.4 cm wide; small tufts of leaves in axils few or none.
Flowers pink-purple, 2-4 cm long, broadly tubular, slightly bilaterally symmetrical, petal lobes bent back, hairy inside; calyx tube 0.2-0.4 cm, lobes to half as long as tube, triangular, tips pointed, flowers in upper axils on stalks 0.1-0.4 cm.
Fruit dry, a rounded capsule 0.4-0.6 cm, seeds dark.
Wetland status: FACW-.
Frequency in NYC: Very infrequent.
Habitat: Open sites in moist to wet soil.