Herbs or subshrubs, annual or perennial. Stems prostrate, decumbent, ascending, erect, or floating, indumentum of simple trichomes. Leaves opposite, sessile or petiolate; blade lanceolate to ovate, ovate-rhombic, or obovate-rhombic, margins entire. Inflorescences axillary or terminal, sessile or pedunculate, several-flowered cylindric spikes or globose heads, without immediately subtending leaves; bracts and bracteoles scarious. Flowers bisexual; tepals 5, distinct; stamens 3–5; filaments connate basally into tube or short cup; pseudostaminodes 5, alternating with stamens; ovule 1; style 1, ca. 0.2 mm; stigma capitate or rarely 2-lobed. Utricles compressed, ovoid or obovoid, indehiscence. Seeds 1, reddish brown, lenticular or ovoid-oblong.

Distribution

Primarily American tropics and subtropics, some in Asia, Africa, and Australia.

Discussion

Species ca. 80 (9 in the flora).

Selected References

Mears, J. A. 1978. The nomenclature and type collections of the widespread taxa of Alternanthera (Amaranthaceae). Proc. Acad. Nat. Sci. Philadelphia 129: 1–21.

Lower Taxa

Alternanthera brasiliana, Alternanthera caracasana, Alternanthera ficoidea, Alternanthera flavescens, Alternanthera maritima, Alternanthera paronychioides, Alternanthera philoxeroides, Alternanthera pungens, Alternanthera sessilis

Key

1	Inflorescences pedunculate, terminal and axillary	> 2
1	Inflorescences sessile, axillary	> 4
2	Bracts not keeled; tepals glabrous	Alternanthera philoxeroides
2	Bracts keeled; tepals pilose	> 3
3	Bracts shorter than to equaling tepals	Alternanthera brasiliana
3	Bracts less than 1/2 as long as tepals	Alternanthera flavescens
4	Pseudostaminode margins fimbriate; anthers 5, oblong	> 5
4	Pseudostaminode margins laciniate, dentate or, entire; anthers 3-5, globose	> 6
5	Tepals rigid, margins coriaceous, glabrous; leaves succulent	Alternanthera maritima
5	Tepals not rigid, margins chartaceous, pilose or hispid; leaves not succulent	Alternanthera ficoidea
6	Tepals monomorphic, hairs not barbed	> 7
6	Tepals dimorphic, hairs barbed	> 8
7	Mature fruit exerted between tepals	Alternanthera sessilis
7	Mature fruit included within tepals	Alternanthera paronychioides
8	Tepals 5-7 mm, sparsely villous; leaf blades usually as broad as long; pseudostaminode margins dentate	Alternanthera pungens
8	Tepals 3-5 mm, densely villous; leaf blades longer than broad; pseudostaminode margins usually entire	Alternanthera caracasana