As per efi thread:
A.bidentata and A.aspera can be differentiated by following key:
Leaves thin, membranous, staminodes toothed, wings of bracteoles 1.5-2mm long……………….. A.bidentata
Leaves thick, scabrid, staminodes fimbriate from margins, wings of bracteoles less than 1mm…. A.aspera
It must be noted that A. coynei is much different from A. dentata and more a gigantic form of A. aspera with larger habit and very long inflorescence often more than 30 cm long and thicker leaves
A.porphyristachya has been named as a var. of A aspera in Mah BSI flora. with description of leaves similar to what you have described for the above species. i.e. glabrous mambranous as against thick velvetty tomentose in A.aspera. but……as you have described ; pattern of staminodes must be the key for distinguishing amongst the two.
Achyranthes species in India:
Achyranthes page with images of species in efloraofindia : 1 post by 1 author.
Pl. go through Achyranthes page with images of species (mainly done by me) in efloraofindia.
If you find any mis-identification, pl. let us know. If anybody can send images of other species of this genera (for incorporation in the website), if any, it will be really nice.
Also, if anybody is interested to take up the activity of inserting images on efloraofindia pages from efloraofindia posts, pl. let us know.