Our only specimens are from an open, wooded slope in Harrison County about 3 miles east of Elizabeth. It was reported from Steuben County by Bradner, but no doubt this report should be referred to Thaspium trifoliatum var. flavum which is found there and which he did not report. Zizia aptera is often confused with Thaspium trifoliatum var. flavum which also has thickened, white, and glabrous margins of the leaflets, but from which it can easily be distinguished because Zizia aptera has a sessile central flower in each umbellule.
Basal lvs and occasionally the lower cauline ones simple, long-petioled, deltoid-ovate or round-ovate to oblong-ovate, cordate at base; cauline lvs once or twice ternate, the lfls lance-ovate to obovate-oblong; rays at anthesis 1-3 cm, at maturity ascending, to 5 cm; fr oblong-ovate, 3-4 mm; 2n=22. Moist meadows and open woods; N.Y. to Man. and B.C., s. to Ga., Mo., and Colo. May, June. Our plants are var. aptera. (Z. cordata)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.