Osmorhiza longistylis is a perennial herb to 1.2 m tall, plant anise-scented, from thick, carrot-like, aromatic roots to 1 cm thick, stem smooth, to finely hairy, sometimes purple.
Leaves alternate, few, the upper stalkless (sessile), the lower stalked, base wide, clasping stem; blade 2-3 times compound, 10-30 cm long, hairy, leaflets 2-10 cm long, 1-5 cm wide (Yatskievych 2006), egg-shaped, margins sharp-toothed to lobed.
Flowers white, somewhat irregular, 5-parted, petals free to 0.2 cm long and wide, but often 1 or 2 longer than the rest (Yatskievych 2006), sepals none; stamens alternating with petals; ovary inferior, 2-parted, each part with one style, 0.2 cm long, longer than petals; fertile and sterile (staminate) flowers mixed; producing nectar; inflorescence sparse, compound-umbrella-shaped, primary rays 3-5, each 2-5 cm long, bracts at base of the primary rays 1-3; secondary rays more numerous than O. claytonii, each with one flower, bracts at base of secondary rays 3-5, ca 0.4 cm long; inflorescence stalk 5-15 cm long (Radford et al. 1968); blooms May-June; visited by butterflies.
Fruit dry, in pairs, parts held together by hair-thin stalks; fruit bristly-ribbed, blackish, linear, 1.5-2 cm long, tip with persistent style 0.3-0.4 cm long, base forming a bristly tail; fruit often persistent on old plant until the following spring cm in fruit, June-Aug. dispersed by clinging to fur or clothing (Matlack 1994); winter plant fragile, soon fallen (Levine, 1995).
Wetland status: FACU-.
Frequency in NYC: Infrequent.
Habitat: Moist woods.
Notes: Very similar to O. claytonii but flowers slightly larger and more numerous on each ultimate umbel, styles longer than petals in flower and to 0.4 cm long in fruit.