Ptilimnium capillaceum is an annual herb 20-80 cm tall, freely branched near top.
Leaves alternate, 4-10 cm long, pinnately divided into diffuse, finely linear segments 0.5-2.5 cm long, usually in threes.
Flowers white small, radially symmetrical, in umbrella-shaped clusters 2-5 cm wide with 5-15 rays; blooming July-Oct.
Fruit dry, small, nut-like broadly egg-shaped 0.2-0.3 cm, 5-ribbed; fruiting Aug-Oct. (Hough 1983).
Wetland status: OBL
Frequency in NYC: Very infrequent.
Habitat: Fresh or brackish marshes, mostly along coast.
Notes: Apiaceae of open sites are eaten by larvae of the black swallowtail butterfly, Papilio polyxenes (Papilionidae) (Tallamy 2003; Pyle 1981).