Plants annual or perennial. Taproots slender to stout, sometimes absent; perennials often with stout, branched caudices, some with adventitious roots from decumbent stems or elongating rhizomes. Stems erect, ± sprawling, or less often decumbent or prostrate, usually branched, terete. Leaves briefly connate proximally, sessile; blade 1- or 3-5-veined, linear to oblong or ovate, apex rounded or obtuse to acuminate. Inflorescences dichasial cymes or thyrses, diffuse (to subcapitate in G. oldhamiana); bracts paired, proximal bracts foliaceous, distal ones smaller, herbaceous with scarious margins; involucel bracteoles absent. Pedicels erect in fruit. Flowers: sepals connate proximally into cup, 1-5 mm, cup green and white, 5-veined, not winged, obconic to campanulate, terete to 5-angled, commissures between sepals veinless, broad, scarious; lobes green at least along midrib, usually ovate to elliptic, equaling or longer than cup, margins white, scarious, apex rounded to obtuse, sometimes mucronate; petals 5, white, pink, or rose-purple, claw poorly differentiated, auricles absent, coronal appendages absent; blade apex entire or shallowly emarginate to 2-fid, nectaries at filament bases; stamens 10, arising with petals from low nectariferous disc; filaments distinct nearly to base; staminodes absent; ovary 1-locular; styles 2(-3), clavate, 1.2-2.5 mm, glabrous proximally; stigmas 2(-3), subterminal, papillate (30×). Capsules globose or ellipsoid-ovoid, opening by 4(-6) slightly distally recurving valves; carpophore absent. Seeds 4-36, brown to black, reniform to snail-shell-shaped, laterally compressed, tuberculate, marginal wing absent, appendages absent; embryo peripheral, curved. x = 17, 12 (Eurasia), 18 (Eurasia); aneuploidy occasional.
Cymes dichasially branched, often diffuse; bracts scarious; cal short, campanulate to turbinate, 5-nerved, with scarious commissures, ebracteate; pet scarcely differentiated into blade and claw, without auricles or appendages; stamens 10; styles 2; capsule globose to oblong, opening by 4 ascending teeth; seeds compressed, subreniform; annual or perennial herbs, none native. 125, mainly temp. Eurasia.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.