Pacif. Railr. Rep. 4(5): 139. 1857.
Herbs, annual, with stinging and nonstinging hairs. Stems usually branched, erect, spreading, or reclining. Leaves opposite; stipules present. Leaf blades ovate to broadly ovate, distal blades sometimes broadly elliptic, margins serrate; cystoliths elongate. Inflorescences axillary, globose, nearly globose, or elongate-racemose or paniculate. Flowers unisexual, staminate and pistillate in loose to dense clusters in same inflorescence; bracts absent. Staminate flowers: tepals 4, distinct, equal; stamens 4; pistillode present. Pistillate flowers: tepals 4, connate, forming persistent saclike structure covered with delicate, hooked hairs and completely enclosing mature, flattened achene; staminodes absent; style absent, stigma tufted, persistent. Achenes subsessile, laterally compressed, ovoid, tightly enclosed in persistent tepals. x = 12.
1 in Calif. and Mexico, 1 in Pacific Islands (Hawaii).
Species 2 (1 in the flora).