1a. Basal leaves usually simple, rarely ternate; leaflet margins crenate-serrate
1b. Basal leaves 1--2-ternate; leaflet margins dentate to serrate.
2a. Leaflet margins finely serrate, teeth (4--)5--10 per cm, apices usually acuminate, sometimes acute; umbel rays (8--)10--21, 1--4(--5) cm; mericarps oblong to ovate, 2--4 x 1--2 mm
2b. Leaflet margins coarsely serrate, teeth (1--)2--3(--4) per cm, apices acute to obtuse; umbel rays 4--10(--12), 4--12 cm (some always at least 5 cm in fruit); mericarps broadly ovate, 3--4.5 x 2--3.5 mm
Herbs, perennial, unpleasant smelling when crushed, 2--11(--15) dm; roots +/- tuberous-thickened. Leaves: basal simple or ternate, cauline ternate; blade ovate to deltate-ovate, suborbiculate, or cordate, coriaceous; leaflets usually simple, sometimes lobed basally, ovate to oblong-obovate or lanceolate, margins toothed. Umbels: axillary and terminal, compound, +/- round-topped, peripheral flowers not different; involucral bracts absent; involucel bractlets present. Pedicels: present, except absent or nearly so for central flower in each umbellet. Flowers: bisexual and staminate (plants andromonoecious); sepals well developed; petals bright to golden yellow; stylopodium absent. Schizocarps: splitting, mericarps oblong to ovate, compressed laterally, not beaked, ribs +/- corky, surface smooth, glabrous; carpophore 2-fid. x = 11.
Species 3 (3 in the flora): North America.
Plants of Thaspium and Zizia can be difficult to distinguish, especially if mature fruits, which are winged in Thaspium and wingless in Zizia, are not available. Thaspium has fibrous roots (versus somewhat thickened in Zizia) and all its flowers are pedicellate (versus the central flower of each umbellet sessile or essentially so in Zizia). Additional characteristics that can be used to distinguish commonly confused species in these genera are given in the species discussions below.
SELECTED REFERENCES Cooperrider, T. A. 1985. Thaspium and Zizia (Umbelliferae) in Ohio. Castanea 50: 116--119. Lindsey, A. H. 1982. Floral phenology patterns and breeding systems in Thaspium and Zizia (Apiaceae). Syst. Bot. 7: 1--12. Weakley, A. S. 2015. Flora of the Southern and Mid-Atlantic States. Working Draft of 21 May 2015. Chapel Hill.