Leaflets: blade apex acute to obtuse. Inflorescence bracts lanceolate to ovate. Petals white (sometimes pinkish), (3-)5-7 (-8) mm. Stamens (6-)7-10 (-14) mm, ± equaling or slightly longer than petals. Seeds roughened. 2n = 20.
Subspecies dodecandra is smaller-flowered than the other subspecies and is most often found in northeastern and midwestern states. `White Spider´ is a cultivar sometimes offered in seed catalogues. Occurrences in New England (except Vermont) probably represent adventives from farther west; this plant is common along weedy roadsides.
Annual herb 20 cm - 0.8 m tall Stem: erect, arching with age, branched, covered with sticky hairs. Leaves: compound with three leaflets (trifoliate), stalked, having an unpleasant odor. Flowers: borne in a many-flowered (fifteen to 30) terminal inflorescence (raceme), each flower subtended by a leaf-like bract and having a purple style. The four petals are white or pinkish, 3.5 - 6.5 mm long, with the upper pair being longer than the lower pair, narrowing to a long claw at the base, and deeply notched to squared at the tip. Stamens ten to 27, pink to purplish, 4 - 10 mm long, not much longer than petals. Fruit: an erect capsule, 2 - 7 cm long, 5 - 10 mm wide, oblong, flattened but slightly inflated, with interconnecting veins and stalked glands, opening from the tip to two-thirds the length, releasing fifteen to 40 or more dull reddish to dark brown seeds (1.7 - 3 mm). Leaflets: 1.5 - 6 cm long, 0.5 - 2 cm wide, lance-shaped to widest above middle or lance-elliptic.
Similar species: The similar Polanisia dodecandra ssp. trachysperma has longer petals (8 - 16 mm) and longer stamens (12 - 30 mm), with the stamens usually much longer than the petals.
Flowering: mid June to early October
Habitat and ecology: This species grows in gravelly soil, often along railroads or along river banks.
Occurence in the Chicago region: native
Etymology: Polanisia comes from the Greek words polys, meaning many, and anisos, meaning unequal, referring to the stamens. Dodecandra means "with twelve stamens."
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
This species grows in very sandy soil and is usually found on sand and gravel bars of streams, along roadsides and railroads, and rarely in fallow or cultivated land along streams. On large sandbars it often forms extensive colonies.