Herbs with opposite, petiolate, entire leaves. Inflorescence a ± slender spike, terminal on the stem and branches, the flowers at first congested and ± patent, finally laxer and often deflexed; bracts deltoid or ovate, the midrib excurrent in a spine. Flowers solitary in the bracts, bibracteolate, hermaphrodite. Perianth segments 4-5, narrowly lanceolate, acuminate, 1-3 (-5)-nerved, aristate with the excurrent midrib, indurate in fruit especially at the base. Bracteoles spinous, the spine furnished at the base with short and free to longer and adnate membranous wings. Stamens 2-5, filaments filiform, monadelphous, alternating with quadrate to broadly quadrate-spathulate pseudo-staminodes, these simple and dentate or fimbriate, or furnished with a variably developed dorsal scale. Style slender, stigma small, truncate-capitate. Ovary with a solitary pendulous ovule, the ovary wall very thin in fruit. Entire flower with bracteoles falling with the ripening of the cylindrical seed, the deflexed bracts persistent.
About 6 species in the warm temperate and tropical regions of the world.
Type species: Achyranthes aspera Linn., Sp. Pl. ed. 1: 204. 1753.
A very difficult genus taxonomically, greatly in need of cytological and experimental investigation; there appear to have been a number of geographical races of, in particular, Achyranthes aspera; these, getting about as weeds, have probably interbred with local populations. The result has been a welter of forms virtually defying orthodox taxonomic treatment.