Astranthus Loureiro; Blakwellia Commerson ex Jussieu (1789), not Scopoli (1777), nor Lamarck (1785); Pierrea Hance (1877), not F. Heim (1891), nom. cons.

Trees or shrubs. Leaves alternate, rarely opposite or verticillate; stipules caducous; usually petiolate; leaf blade pinnate-veined, margin with glandular teeth, rarely entire. Flowers bisexual, epigynous, small, in terminal or axillary, many flowered racemes or panicles, inserted singly along rachis, or in sessile to shortly pedunculate fascicles; bracts small, caducous or persistent; pedicels slender in flower, articulate at or above middle. Sepals and/or petals often accrescent after anthesis. Calyx tube obconic, adnate to lower 2/3 of ovary and later to lower 2/3 of capsule; sepals (4 or)5-8(-12), spreading, linear, oblong, or obovate-spatulate, persistent. Petals inserted at rim of calyx tube, usually isomerous with and similar to sepals, alternating with them. Disk glands 1 opposite each sepal, rarely more or fewer, small, fleshy, ± globose and hairy. Stamens inserted singly or in groups before each petal, alternating with disk glands and inserted between them, usually finally overtopping perianth; filaments free, filiform; anthers subglobose, small, dorsifixed. Ovary semi-inferior, only upper conic part free above adnate calyx tube, 1-loculed; placentas 2-6(-8), with (1-)3-7 ovules near apex of each placenta; styles 2-5(-7), filiform, free or united in lower 1/3 or less, free parts divergent, usually finally overtopping perianth; stigmas capitate to punctiform, small. Capsule obconic, small, for most of its length enclosed in adnate calyx tube and persistent perianth segments, leathery, apex 2-8-valvate; styles ± persistent. Seeds 1 to few.

In Chinese species: disk glands 1 or 2 opposite each sepal; stamens 1 opposite each petal; capsules to 7 mm.

Much uncertainty remains in the taxonomy of Chinese Homalium. Further gatherings and detailed study are recommended to establish reliable diagnostic characters (especially comparing the perianth in flower and fruit) and a stronger taxonomic framework. Where possible, descriptions of taxa in this account have been extended to include detail of perianth indumentum, which can be a useful character at species level. Sepal and petal lengths (both absolute and relative) are sometimes less useful, because of their accrescent nature. Inflorescence type (panicle vs. raceme) needs to be used with caution: apparent racemes sometimes have lateral branches although these are very short (to ca. 5 mm); false panicles occur when the leaves subtending all axillary racemes on a lateral branch are lost.

See also the four inadequately known species briefly described at the end of Homalium.

Between 180 and 200 species: tropical regions of both hemispheres; ten species (six endemic) in China; four additional species (all endemic) are poorly known.