Clethra L.

Trees or shrubs, evergreen (Mal. spp.); leaf-scars large. Leaves crowded towards the end of the shoots, spiral, simple, exstipulate, serrate with glandular teeth, often with an apical gland, more rarely entire; nerves a little decurrent along the midrib, both midrib and nerves ± impressed above, ± prominent beneath. Indumentum of branchlets, leaves and inflorescences consisting of simple, and/or long, fascicled and ± patent, and/or minor, ± depressed stellate hairs. Flowers bisexual, regular, 5(-6)-merous. Inflorescences sometimes simple solitary terminal racemes, but mostly consisting of a terminal raceme and several lower approximate racemes, each of the latter from the axil of a ± reduced or caducous leaf, thus forming together a panicle-, fascicle-or umbel-like inflorescence; bracts mostly caducous during anthesis, rarely subpersistent. Calyx lobes 5(-6), persistent, quincuncially imbricate, united at the base only. Petals 5(-6), generally free, sometimes cohering to some degree, alternate with the calyx lobes, rather early caducous, generally sweet-scented. Stamens 10(-12) in 2 whorls of 5(-6), the outer whorl opposite the petals, the inner one opposite the calyx lobes; filaments adnate to the corolla at the extreme base; anthers dorsifixed, overturned outwards in bud, erect in anthesis, introrse, upper part of cells ± divergent, opening with apical, slit-like pores; pollen grains single, tricolporate, psilate. Ovary superior, 3-celled, with axile placentation; ovules ∞, small, anatropous; style simple, mostly shortly, very rarely hardly divided into three apical lobes, sometimes more deeply so and trifid, each lobe stigmatic at the top. Fruit a 3-valved, loculicidal capsule, the septae of which become loose from the persistent central axis, subtended or ± enclosed at maturity by the persistent calyx. Seeds ∞, small, subovoid to irregularly angular or subtrigonous, with a foveolate-reticulate testa (all Mal. spp.). Endosperm fleshy. Embryo cylindrical.

Clethra occurs mainly in the lower and upper montane primary (and also secondary) forest. As to climate, the genus prefers the wet montane tropical and subtropical zone, though it extends far into the northern temperate zone, in North America to about 45°, in Japan to about 42° N, whilst its southern limit is about 29° S in SE. Brazil. As the majority of the Ericales, Clethras have preference for acid soils. They occur in Malesia from sea-level to about 3000 m; and up to c. 3800 m in Szechuan and Yunnan, and in the Andes. They are light-demanding, remain sterile in dense forest, and flower in forest borders with open vegetation or exclusively in the latter, also in light secondary plant communities.

Uses. Temperate species of Clethra, mainly from North America, Madeira and Japan, much less from China, are cultivated as ornamentals in many parts of the world. Not a single species from Malesia so far has been introduced in Botanic Gardens.