Description from Flora of China
Herbs or subshrubs. Stem with conspicuous nodes; branches opposite. Leaves opposite, petiolate. Spikes terminal or axillary, erect. Flowers reflexed or spreading, perfect, with 3 bracts; midvein of bracteoles spiny, long, excurrent. Tepals 4 or 5, membranous, apex awn-pointed, rigid in fruit. Stamens 5, rarely 4 or 2, shorter than perianth; filaments connate into a short cup at base, pseudostaminodes fringed; anthers 2-loculed. Ovary oblong; style linear, persistent; stigma capitate. Utricles ovoid-oblong, ovoid, or subglobose, falling off with tepals and bracteoles. Seed oblong, lenticular.
The two species Achyranthes aspera and A. bidentata are highly variable. Further study might show A. longifolia to be merely a variant of A. bidentata.
Achyranthes megaphylla Y. H. Li (Guihaia 9: 26. 1989, not Standley, 1917) was described from Yunnan and A. ogatae Yamamoto (Icon. Pl. Formosan., Suppl. 3: 23. 1927) was described from Taiwan. We have seen no specimens of either taxon and are therefore unable to treat them in this account. Further revisionary study is necessary.
About 15 species: tropical and subtropical regions; three species in China.