Lycopus uniflorus is a perennial herb 20-100 cm tall, stems 4-sided, from tuber-bearing stolons, a single stem arising from each tuber the following year.
Leaves opposite, essentially stalkless (sessile), 2-6 cm long, 0.5-3 cm wide (Radford et al. 1968), lance-shaped, tapered at both ends, light green, margin with few coarse teeth.
Flowers white, corolla about twice as long as calyx, petal-lobes 5 due to top lobe being notched, flaring, calyx 0.15 cm long, lobes 5, about equal to tube; stamens purple, longer than corolla; flowers embedded in small bracts in tight circular tufts around stems at nodes; blooms July-Sept.
Fruit dry, of 4 nutlets, larger than persistent calyx, wedge-shaped, one side flat, other side rounded.
Wetland status: OBL.
Frequency in NYC: Very infrequent.
Habitat: Open, wet soil, swamps, ditches.