Frequently confused with Thaspium, but material with young or mature fruit is easily distinguished not only by the presence of ribs (rather than definite thin wings) on the mericarps but also by the presence of a more or less sessile central fruit in at least some umbellets. In Thaspium, the central flowers in all umbellets are pediceled and staminate, leaving only the marginal and pediceled bisexual flowers to develop fruit.

1. Basal leaves simple, with cordate blades; cauline leaves with 3 leaflets.

Z. aptera

1. Basal leaves compound, like the cauline, with (3-) 5-11 leaflets.

Z. aurea