From the closely related heath family the clethras are distinguished by having the five parts of the corolla so deeply divided that they appear to be separate petals. They are small trees or shrubs, all the hardy ones deciduous, but the tender ones all or mostly evergreen. Leaves alternate. Flowers white, fragrant, usually produced in racemes or panicles near the end of the shoot; stamens ten. Seed-vessel a capsule enclosed by the persistent calyx, and carrying many seeds.
Of the hardy species, three come from America, four from Eastern Asia. They all like a peaty soil, and are useful for flowering late in the season. Propagated by seeds, cuttings, and layers. The cuttings are best made in August, of side shoots 3 or 4 in. long, with a heel of older wood, and placed in gentle bottom heat.