Plants moderate, clustered, shrubby. Stems branched or unbranched, procumbent or ascending, covered with leafbases or becoming striate or smooth with age. Leaves: sheath fibers soft; petiole base not split; petiole armed with fine teeth, sometimes only at base of petiole; abaxial hastula not well -developed, obtuse; adaxial hastula usually well -developed, obtuse; costa absent; blade palmate; plication induplicate; segments lanceolate, basally connate, apices acute or 2-cleft; cross veins conspicuous. Inflorescences axillary within crown of leaves, paniculate, ascending, about as long as leaves, with 2--3 orders of branching; main axis bearing 2 peduncular bracts above prophyll; rachillae pubescent. Flowers bisexual, borne singly or in pairs along rachillae, sessile; perianth 2-seriate; calyx cupulate, ,3-lobed; petals 3, imbricate, elliptic, reflexed, alternate with outer whorl of stamens, basally adnate to filaments; stamens 6 in 2 whorls; filaments narrowly triangular, basally connate; anthers dorsifixed, versatile; pistils 3, distinct basally, glabrous; ovules 3, only 1 developing into fruit; styles connate, elongate, glabrous; nectaries 3, septal; stigma minutely 3-lobed, dry. Fruits drupes, ellipsoid; exocarp black, smooth; mesocarp blackish; endocarp brown, bony. Seeds brown, ellipsoid, with conspicuous longitudinal raphe; endosperm bony, homogeneous; embryo nearly basal; eophyll undivided, lanceolate. nx = 18. Serenoa, with a single polymorphic species, is endemic to the southeastern United States. It grows in a variety of habitats and communities including pine flatwoods, sand-pine scrub, and coastal sand dunes. It sometimes occurs in vast stands nearly excluding all other understory shrubs. The relationships of Serenoa are with Acoelorraphe, of the Caribbean Basin (N. W. Uhl et al. 1995), and perhaps Brahea, of Mexico and Central America (N. W. Uhl and J. Dransfield 1987).