Decodon verticillatus is a perennial herb from woody base, bark of submerged stems thick, spongy; stems slender 1-3 m long, arching, 4-angled, rooting at tips, extensively colonial.
Leaves whorls of 3-4, sometimes opposite, petiole short, blade 5-15 cm long, 1-4 cm wide, lance-shaped.
Flowers pink-purple, radially symmetrical, 4-5 parted, petals 1-1.5 cm, long, narrowed at base, attached to a rounded floral base (hypanthium), sepals short, triangular, attached to hypanthium alternating with longer, linear structures; stamens 8-10, of two sizes, all longer than petals; inflorescence of small, dense upper-axillary clusters along stems; blooms July- Aug.
Fruit dry, a 3-parted capsule 0.5 cm wide, seeds sharply angled.
Wetland status: OBL.
Frequency in NYC: infrequent. except in Richmond Co. (Staten Island).
Habitat: Open, shallow water or saturated soil of ponds and sunny vernal pools. Soil pH 5.2-7.2 Tolerant of saturated soil, intolerant of salt, drought. Able to resprout after fire (USDA, NRCS 2006).
Notes: Same family as the invasive European aquatic annual plant Lythrum salicaria. There is some concern that the insects imported to control purple loosestrife may also attack Decodon.