Perennial herbs up to 0.55 m m tall, glabrous, not glaucous, with stems erect from decumbent to prostrate and rooting base, radiating from taproot, unbranched below inflorescence or usually branched at the base and sometimes from intermediate nodes, with dark (black or reddish) to amber or pale glands on leaves, sepals and anthers and sometimes stem and petals. Stem narrowly 2(4)-lined to terete, eglandular or with dark (black and amber to reddish) glands on raised lines and surface. Leaves opposite, decussate, sessile or subamplexicaul, free, persistent, chartaceous, usually auriculate; lamina entire or gland-fringed, with venation pinnate; laminar glands pale and sometimes black and sessile or on long cilia, punctiform or sometimes absent (in 2. H. aucheri). Inflorescence 1–c. 50-flowered, with branching mainly monochasial, without or with 1-4 subsidiary branches; bracts and bracteoles auriculate (except in 2. H. aucheri). Flowers stellate, homostylous. Sepals 5, free or slightly connate, usually ± imbricate, persistent, erect in fruit, with margin glandular-laciniate, -ciliate or -tuberculate; veins 3–5; laminar glands pale, linear to punctiform, and sometimes black, punctiform; marginal glands black or amber, intramarginal or on denticles to fimbriae, irregular. Petals 5, persistent, erect but not twisting after flowering, without apiculus; margin entire or crenate to glandular-ciliate; laminar glands pale and sometimes black, linear to punctiform; marginal glands black, regular or distal, sometimes almost absent. Stamen fascicles ‘3’(5), persistent, with stamens totalling 30–80; anther gland amber or black (H. thasium); pollen type X. Ovary with 3(5) axile placentae, each ∞-ovulate; styles 3(5), diverging; stigma narrow. Capsule 3(5)-valved, subcoriaceous, with valves longitudinally narrowly vittate. Seeds cylindric, not carinate or appendiculate; testa shallowly reticulate to foveolate-scalariform.