Perennial herbs up to 0.8 m. tall, glabrous to pubescent or scabrid or rarely with branched glandular emergences (20. thymopsis), often glaucous, with stems erect or decumbent at the base from taproot, rarely rooting (7. hyssopifolium), usually with procumbent to ascending basal sterile shoots and axillary branches (often condensed), with dark (black) glands on petals, usually on sepals, sometimes on stems and leaves, but not on anthers or capsules. Stems 2-lined, usually glandiferous. Leaves opposite, decussate, sessile or shortly petiolate, free or very rarely united, persistent, subcoriaceous to herbaceous; lamina entire with venation pinnate or 1-nerved; laminar glands pale and rarely dark; intramarginal glands pale or very rarely some dark (11. apiculatum, 23. asperulum); ventral glands absent. Inflorescence (1) few- to ∞-flowered, with branching monochasial after 1st (or rarely 2nd) flower, from 5–15 nodes, often with flowering branches from up to 4 nodes below; buds erect. Flowers stellate, homostylous. Sepals 5, unequal to equal, free or up to 0.6 united, imbricate or not, persistent, erect in fruit, with margin entire to irregularly or regularly gland-fringed or denticulate; veins 3–5, not branched; laminar glands pale or very rarely black, linear to punctiform; marginal glands black or absent. Petals 5, persistent, unguiculate, spreading or deflexed after flowering, without apiculus, occasionally red-veined or red-tinged or (27b. capitatum var. capitatum) wholly suffused red; margin with sessile glands or glandular-ciliate; laminar glands pale or very rarely dark (23. asperulum), all punctiform or some shortly striiform or very rarely elongate-striiform (19. scabrum) or linear (20. thymopsis); marginal glands black, globose to ellipsoid or obconic. Stamen fascicles ‘3’ (i.e. 2+2+1), persistent, with stamens totalling 25–60, basally united in each fascicle; anther gland amber; pollen types X–XI, grains often partly irregular. Ovary with 3(4) axile placentae, each ∞–6-ovulate; styles 3(4), divergent from discrete bases; stigmas small or slightly capitate. Capsule 3(4)-valved, coriaceous to papyraceous, longitudinally vittate or rarely lateral vittae swollen (19. scabrum and 22. hirtellum in part), very rarely dehiscing as few- to 1-seeded cocci (26. olivieri). Seeds cylindric, not carinate or appendiculate; testa papillose.