Herbs, rhizomatous, not stoloniferous (± stoloniferous in B. intermedia). Flowering stems erect, leafy, 10-130 cm, densely stipitate-glandular and eglandular-pubescent. Leaves in basal rosette and cauline; cauline leaves similar to basal, gradually reduced distally to sessile bracts; stipules present; petiole densely stipitate-glandular; basal leaf blades reniform to reniform-orbiculate or cordate, shallowly lobed to deeply cleft, base cordate, ultimate margins crenate to serrate, apex acute or rounded, surfaces stipitate-glandular, adaxial surface grooved over veins; venation palmate. Inflorescences compound, dichasial cymes, terminal from terminal bud in rosette, branches (3-)5-20(-30)-flowered, bracteate. Flowers ± radially symmetric; hypanthium adnate 1/2-5/6 to ovary, free from ovary 0.7-3 mm, usually green, sometimes purple; sepals 5, green to purple; petals 5, white (sometimes with pink veins in B. richardsonii); nectary tissue encircling base of styles at junction of ovary and free hypanthium; stamens 5; filaments linear to subulate; (anthers apiculate or obtuse); ovary 2/3 to completely inferior, 2-locular, carpels connate proximally; placentation axile; styles 2; stigmas 2. Capsules 2-beaked. Seeds (ca. 50-500), usually black, (brown in B. richardsonii), ellipsoid, tuberculate (smooth in B. richardsonii). x = 7. The Japanese species is Boykinia lycoctonifolia (Maximovicz) Engler, which, based on its morphology, seems to be most closely related to B. aconitifolia.
Fls perfect, regular, ±epigynous with a prolonged, deeply cupulate or campanulate hypanthium bearing the sep, pet, and stamens at its margin; pet obovate or spatulate, deciduous; stamens 5, opposite and shorter than the sep; carpels 2, connate below to form a bilocular ovary with numerous ovules on axile placentas, tapering above into the 2 short, distinct stylar beaks that eventually dehisce ventrally; stigmas capitate; capsule largely contained within the persistent hypanthium; seeds wingless; rhizomatous perennial herbs with basal and alternate, long-petioled, ±stipulate, palmately lobed lvs and panicled cymes of small white fls. 7, N. Amer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.