Herbs, perennial or annual. Stems erect to ascending. Leaves opposite, petiolate; blade elliptic, ovate to orbiculate, or broadly rhombate, margins entire. Inflorescences terminal and axillary, pedunculate, elongate, many-flowered, simple spikes or few-branched panicles; flowers crowded together at tips, becoming more widely spaced toward base. Flowers bisexual, often becoming deflexed with age; tepals 4 or 5, basally connate, without ornamentation, coriaceous, becoming indurate in fruit, ± glabrous; filaments basally connate into short tubes or cups; anthers 4-locular; pseudostaminodes 5; ovary obovoid or turbinate; ovule 1; style elongate; stigma 1, capitate. Utricles enclosed by and falling with indurate tepals, elliptic or cylindric, membranous, indehiscent. Seeds 1, inverted, obovoid or ovoid, smooth.
c and se United States, Mexico, West Indies, Central America, South America, tropical, subtropical, and warm-temperate regions of the Old World.
Species 8–12 (2 in the flora).
The groups of plants referred to as Achyranthes and Alternanthera have been subject to considerable nomenclatural confusion, primarily because P. C. Standley (1915) designated Achyranthes repens Linnaeus as the lectotype species of Achyranthes. As a result, species that had been placed in Achyranthes were transferred to Centrostachys Wallich, and species that had been in Alternanthera were transferred to Achyranthes. A. A. Bullock (1957; see also R. Melville 1958) showed that Standley’s lectotypification was incorrect and that the type species of Achyranthes is Achyranthes aspera Linnaeus. The generic concepts of Achyranthes and Alternanthera then returned to those prior to 1915.