Perennial herb 15 cm - 0.9 m tall Leaves: usually two, long-stalked, with three leaflets (rarely five). The leaflets are more or less stalkless, to 30 cm long and 20 cm wide, with the terminal leaflet elliptic to broadly egg-shaped and the lateral leaflets somewhat asymmetrical and sometimes lobed or divided. Lower leaf surface glossy. Inflorescence: of many tiny flowers borne tightly clustered on the bottom half of a spike with a very fleshy axis (spadix), with male flowers above female flowers. The spadix is yellow, 3 - 9 cm long, and cylindric (rarely club-shaped) with a blunt tip. The leaf-like sheath (spathe) surrounding the inflorescence forms a fluted green tube sometimes striped with purple or white, having a rim 1 - 3 mm wide, and expanding near the tip to form a long tapering hood over the inflorescence. Fruit: a 6 - 15 mm long cluster of nearly spherical red berries, each with one to three seeds reaching 3 - 5 mm across.
Similar species: Arisaema triphyllum ssp. triphyllum differs from Arisaema triphyllum ssp. stewardsonii by having a whitish waxy coating on the lower leaf surface, a 4.9 - 9 mm wide spathe rim, a green spathe hood that sometimes has purple (but not white) stripes, and a usually club-shaped spadix tip. Its range is also widespread across the Chicago Region.
Flowering: mid April to mid July
Habitat and ecology: Swamps, marshes, floodplains, and moist areas.
Occurence in the Chicago region: native
Etymology: Arisaema comes from the Greek words aron, meaning Arum, and haima, meaning blood, referring to the blotchy red leaf color of some species. Triphyllum means three-leaved. Stewardsonii was named after Stewardson Brown (1867 - 1921), one of the plant's discoverers.