[*] Calyx in the fertile flowers of 2–5 separate or nearly separate sepals.
[+] Plant beset with stinging bristles.
8. Urtica. Sepals 4 in both fertile and sterile flowers. Achene straight and erect, enclosed by the 2 inner and larger sepals. Stigma capitate tufted. Leaves opposite.
9. Laportea. Sepals 5 in the sterile flowers, 4 in the fertile, or apparently only 2. Stigma long-subulate. Achene very oblique, deflexed, nearly naked. Leaves alternate.
[+][+] Plant wholly destitute of stinging bristles. Leaves alternate.
10. Pilea. Sepals 3 or 4, those of the fertile flowers unequal, all or all but one small. Achene partly naked, straight and erect. Stigma pencil-tufted. Smooth and shining.
[*][*] Fertile calyx tubular or cup-shaped, enclosing the achene. Unarmed.
11. Bœhmeria. Flower-clusters spiked, not involucrate. Style long and thread-shaped, stigmatic down one side. Leaves opposite, serrate.
12. Parietaria. Flowers in involucrate-bracted clusters. Stigma tufted. Leaves alternate, entire.
1. ÚLMUS, L. Elm.