Heracleum maximum is a stout perennial herb to 3 m tall, stems single below inflorescence, ribbed, sometimes hairy.
Leaves alternate, leaf stalks broadly sheathing stem, almost pouch-like, pinched in and lobed at top, blade 3-parted, to 30 cm long and wide, leaflets lobed and toothed, sparsely hairy above, densely ffine-hairy below lateral leaflets asymmetrical.
Flowers white (occasionally green), 0.5 cm wide, petals 5, tips curled inward, sepals none; infflorescence umbrella-like, of several compound umbels on long, stout stalks, principle umbels to 20 cm wide at flowering with 15 to 30 rays, wider in fruit, terminal umbels ca 2.5 cm wide; blooms June-July.
Fruit flattened, broadly winged, obovate or heart-shaped, often notched at top, to 1.2 cm long, stalks to 2 cm.
Wetland status: FACU-.
Frequency in NYC: Very infrequent.
Habitat: Rich, moist soil, ditches and open floodplains, soil pH 5.4-7.3 (USDA, NRCS 2006).
Notes: Apiaceae of open sites are eaten by larvae of the black swallowtail butterfly, Papilio polyxenes (Papilionidae); (Tallamy 2003; Pyle 1981).