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.
North America, nw Mexico, e Asia (Japan).
Neoboykinia H. Hara; Therofon Rafinesque
Species 7 (6 in the flora).
The Japanese species is Boykinia lycoctonifolia (Maximovicz) Engler, which, based on its morphology, seems to be most closely related to B. aconitifolia.
|1||Inflorescence branches 3-flowered; seeds smooth.||Boykinia richardsonii|
|1||Inflorescence branches 5-30-flowered; seeds tuberculate||> 2|
|2||Leaf blades usually orbiculate-cordate, sometimes reniform, lobed to 1/2 their lengths; stipules of cauline leaves expansions from petiole base||> 3|
|2||Leaf blades usually reniform, rarely cordate, lobed to 1/2-3/4 their lengths; stipules of cauline leaves foliaceous or expansions from petiole base||> 4|
|3||Petals 2-3 times as long as sepals; basal leaf blades usually 3-9-lobed.||Boykinia occidentalis|
|3||Petals shorter than or to 1.5 times as long as sepals; leaf blades shallowly and indistinctly lobed.||Boykinia rotundifolia|
|4||Hypanthia saucer-shaped; petals suborbiculate to ovate, base contracted to claw, margins undulate.||Boykinia major|
|4||Hypanthia campanulate to turbinate; petals ovate to spatulate, base tapered to claw, margins plane||> 5|
|5||Rhizomes usually underground, not usually stoloniferous; stipules of cauline leaves usually expansions from petiole base, fringed with brown hairs, sometimes foliaceous; nectaries green.||Boykinia aconitifolia|
|5||Rhizomes proliferating above ground, stoloniferous; stipules of cauline leaves usually foliaceous; nectaries greenish yellow.||Boykinia intermedia|