Clethra is a genus of flowering shrubs or small trees erected as a genus by Linnaeus in 1753.
Clethra is one of two genera in the family Clethraceae (the other being Purdiaea). The species may be evergreen or deciduous, and all bear flowers in clusters (inflorescences), which correspond to racemes or panicles. The flowers are quite small, white or pinkish, and each bear five free petals, numerous stamens, and a three-chambered seed capsule. The leaves, simple, ovate, and alternate or opposite, bear characteristic stellate hairs. The seeds are very small and numerous.
Distribution
Clethra species are native to a variety of habitats, including swamps, woodland, and rocky sites from temperate to tropical climates in eastern and southeastern Asia, Malesia, North and South America, and one species (C. arborea) on the Atlantic island of Madeira.
Fossil record
Several fossil fruits and seeds of †Clethra cimbrica have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.
by Else Marie Friis, The Royal Danish Academy of Sciences and Letters 24:3, 1985
Species
The number of species accepted varies between different authorities depending on taxonomic interpretation, but with a recent trend to reduce the number recognised as distinct. The recent Flora of China (series) has cut the number accepted for China from 35 to seven species, and the US Department of Agriculture recognises only two in the United States, synonymising C. tomentosa with C. alnifolia. The following are accepted by the World Checklist of Selected Plant Families:
Clethra acuminata – mountain pepper bush; S Appalachians (Alabama to Pennsylvania)
Clethra alcoceri – Hidalgo, Jalisco
Clethra alexandri – Jamaica
Clethra alnifolia – sweet pepper bush or summer sweet; S + E United States (Texas to Maine)
Clethra arborea – lily of the valley tree; Madeira, Canary Islands†, Azores
Clethra arfakana – New Guinea
Clethra barbinervis – Japanese sweet...
