Steven E. Clemants in Flora of North America (vol. 4)
annual or perennial.
ascending, decumbent, prostrate, or erect.
opposite, sessile or petiolate; blade ovate to obovate, not fleshy, margins entire, long-pilose abaxially and sometimes adaxially.
terminal and/or axillary, sessile, subglobose heads, often subtended by involucres of sessile leaves; bracts and bracteoles thin.
bisexual; tepals 5, connate proximally; stamens 5; filaments connate basally into tube; pseudostaminodes absent; ovule 1; style 1, 1.5-4 mm; stigmas 2(-3), subulate or filiform.
included in tepals, stramineous, ovoid or oblong, somewhat compressed, membranous, usually indehiscent.
1, lenticular, subglobose, to ovoid, smooth.
Species within checklist: