Herbs [subshrubs], perennial, from tough, short rhizomes [rhizomes absent]. Leaves basal and cauline, basal leaf much larger [all leaves cauline], petiolate; cauline leaves alternate. Leaf blade pedately or palmately compound or deeply parted [undivided], lobes narrowly elliptic to oblanceolate or lanceolate, margins sharply toothed [entire]. Inflorescences terminal, 3-4-flowered cymes, to 25 cm or flowers solitary or paired; bracts ±leaflike, divided, not forming involucre. Flowers bisexual, radially symmetric; sepals persistent in fruit [not persistent], 5, yellowish green [white, pink, or purple], plane, ovate to elliptic, 19-30(-50) mm; petals 5-15, distinct, green or brown, funnel-shaped, ± 2-lipped, clawed, 4-8 mm; nectary in center of 'funnel'; stamens 30-60; filaments filiform; staminodes absent between stamens and pistils; pistils [2-]3-6[-10], simple, proximally connate [distinct or completely connate]; ovules several per pistil; style present. Fruits follicles [capsules], aggregate, sessile, oblong, sides with prominent transverse veins; beak terminal, straight, 5-15 mm. Seeds usually ± carinate. x = 8. Although other species of Helleborus are grown as ornamentals, only the green-flowered H . viridis appears to persist after cultivation. Helleborus niger Linnaeus (Christmas-rose) is a more popular ornamental because of its showy, white to pinkish flowers. It does not appear to persist away from cultivation; it was reported as an escape in 1880 at Sennet, New York, and in 1919 in Washtenaw County, Michigan (R. S. Mitchell and J. K. Dean 1982; E. G. Voss 1972+, vol. 2). Helleborus niger can be distinguished from H . viridis by its flower color and its simple, distal cauline leaves with entire margins. Both living and dried plants of all species of Helleborus are extremely poisonous. Plants contain a cardiac glycoside (helleborin), which acts directly on the heart muscle, causing convulsions, delirium, and sometimes death. Poisoning from contaminated hay has been known to cause livestock fatalities in some areas (R. S. Mitchell and J. K. Dean 1982).
Sep 5, large, petaloid; pet none; stamens numerous, the outer 8-10 modified into staminodes, short, upcurved, basally clawed, distally clavate or obovoid, hollow and somewhat 2-lipped; pistils mostly 3 or 4, with erect, slender style; fr follicular; poisonous perennial herbs with alternate, palmately cleft (or the upper entire) lvs and large white, green, or purple fls terminating the stem and branches. 20, Eurasia.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.