1 Styles 1.5× or more as long as the calyx; umbellets dimorphic – some contain both perfect and staminate flowers, while others contain staminate flowers only (except sometimes S. canadensis var. grandis, which may have polygamous umbellets only); larger leaves 3-7-lobed.

  2 Calyx lobes 0.4-0.7 mm long, deltoid, flexible or weak in texture, the apices acute to obtuse; petals yellowish green, much longer than the calyx

  2 Calyx lobes 0.7-2.0 mm long, narrowly triangular to subulate, rigid in texture, the apices acute-acuminate; petals white or greenish-white, equal to or slightly longer than the calyx.

    3 Styles about 1.5× as long as the calyx, inconspicuously exserted from between the calyx lobes and recurved; umbellets usually polygamous (rarely some staminate only); polygamous umbellets with 6-18 flowers (3 perfect and 3-15 staminate); fruit with a short but distinct pedicel 0.5-1.0 mm long; bases of fruit bristles dilated but not bulbous, often minutely papillose

    3 Styles > 2× as long as the calyx, conspicuously exserted from the calyx and recurved; umbellets dimorphic, some polygamous and others staminate only; polygamous umbellets with 12-120 flowers (3-4 perfect and the remainder staminate); fruits sessile to subsessile; bases of fruit bristles prominently bulbous, with a minutely warty-reticulate surface pattern

1 Styles shorter than (or rarely as long as) the calyx; umbellets usually monomorphic (all containing both perfect and staminate flowers), with staminate flowers 1-7 per umbellet; larger leaves 3-foliolate (the lateral leaflets often deeply lobed) or rarely 5-foliolate.

      4 Sepals on mature fruit somewhat spreading, loose, inconspicuous and immersed in the adjacent fruit bristles, the tips of the sepals acute or narrowly acute, straight; pedicels of staminate flowers 1-2 (-3) mm long; [collectively widespread in our area].

        5 Plant a perennial, from thickened, cordlike roots; umbellets with 7-9 flowers (3 perfect and 4-6 staminate)

        5 Plant a biennial, from slender, fibrous roots; umbellets with 4-6 flowers (3 perfect and 1-3 staminate).

          6 Basal leaves (3.8-) 4.3- (mean 5.7) -7.0 (-8.1) cm across, thick in texture; leaf teeth stiff, sharp, and prominently whitened, 0.5- (mean 0.7) - 0.8 (-0.9) mm long (measured from tip to darkened base of spine); [of the Coastal Plain in our area]

          6 Basal leaves (6.6-) 7.0- (mean 8.5) - 9.2 (-9.7) cm across; leaf teeth weak, hyaline, 0.3- (mean 0.4) -0.5 (-0.6) mm long; [collectively widespread in our area, mostly not in the Coastal Plain south of VA].

             7 Largest leaflet of basal and lower stem leaves 3.5-8.0 cm long and 1.5-4.0 cm wide; triads of fruits 0.7-0.9 cm wide; plants to 1 m tall; [widespread in distribution]

             7 Largest leaflet of basal and lower stem leaves 5.5-13.5 cm long (mean 8.5) and 2.5-6.0 cm wide (mean 3.5); triads of fruits 0.8-1.3 cm wide; plants to 2 m tall; [mainly northern and montane in distribution]