Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls perfect (seldom some of them pistillate); cal persistent, mostly 2–5-parted (most commonly 5-, less often 3-), the short, usually blunt segments commonly incurved over the fr (cal only shallowly lobed in one sp.); stamens 1–5, typically isomerous with the cal-lobes; styles 2(–5); fr laterally compressed (the seed erect) or more often flattened across the top (the seed horizontal), thin-walled, the pericarp often adherent to the ± lenticular seed; embryo annular; ours herbs (most spp. annual) with entire or toothed to ± deeply lobed lvs and small, greenish to reddish fls, these in most spp. sessile in glomerules (the glomerules either axillary or in terminal spike-like or panicle-like infls), but in other spp. in compact cymes that may collectively form a thyrse, or otherwise disposed. (Blitum, Roubieva) 100+, cosmop.