Perennial herbs or very rarely suffrutices up to 1.2 m tall, with stems erect to prostrate, glabrous, without or with dark (black or very rarely reddish) glands; branching lateral, from upper or most nodes. Stems 4-2-lined or -winged when young, remaining so or becoming terete, eglandular or with glands confined to the lines or not. Leaves opposite or abnormally 3-whorled, decussate, sessile to shortly pseudopetiolate, free, persistent; lamina entire with venation pinnate, closed, with tertiary reticulation dense to lax and obscure; laminar glands punctiform or rarely shortly striiform, equal or unequal; intramarginal glands black or occasionally also pale; ventral glands absent. Inflorescence 1-c. 70-flowered with branching dichasial-monochasial from 1-4 nodes, often with subsidiary branches from lower nodes; bracts and bracteoles foliar or reduced, persistent. Flowers stellate, homostylous. Sepals 5, free or united at base, persistent, erect to recurved in fruit, with margin entire or denticulate to glandular-ciliate; veins 3-5(-7); laminar glands pale and/or dark, linear to punctiform; marginal and/or intramarginal glands dark and/or very rarely pale or rarely absent. Petals 5, persistent, erect but not twisting after flowering, without apiculus; margin entire to crenate or eroded-denticulate to ciliate; laminar glands linear to punctiform, pale and/or dark; marginal glands dark, immersed to ± prominent, or absent. Stamen fascicles '3' (i.e. united 2+2+1), persistent, with stamens totalling 20-c. 100; filaments basally united; anther gland dark or rarely amber; pollen types IV?, X. Ovary with 3(4) completely or almost completely axile placentae, each ¥-ovulate; styles 3(4), divergent from discrete bases; stigma narrowly capitate or narrow. Capsule 3(4)-valved, chartaceous, with valves longitudinally vittate or sometimes ± laterally vittate to vesiculate, pale. Seeds cylindric, not carinate or appendiculate; testa scalariform-reticulate to finely foveolate.
Basic chromosome number (x). 8; ploidy 2, 4 (rarely 3, 5, 6).
Various; 0-3150 m.
Macaronesia, Europe (except extreme north), north-west Africa, south-west Asia (mesophytic regions) east to north-west India (Uttar Pradesh), central Asia, southern Siberia, north-west Mongolia, Korea, China (except the south-east, Tibet, Tsinghai and E. Xinjiang), Japan, western Canada, western U.S.A., north-west to central Mexico. Represented in many other parts of the world by H. perforatum as an introduction.
42 species in 2 subsections, one with 2 series (for infraspecific taxa and hybrids, see subsectional descriptions).