Key for Amaranthus L.

1Dioecious; tepals of female flowers absent
1'Monoecious; tepals of female flowers present (3-5 per flower)
2Plants armed with axillary spines
2'Plants unarmed
3Leaves strongly emarginate or bilobed at apex
3'Leaves neither strongly emarginate nor bilobed at apex
4Tepals of female flowers 3; stamens 2-3
4'Tepals of female flowers 5; stamens 5
5Terminal inflorescence 5-20(-25) cm long; tepals of female flowers equal; utricle roughly wrinkled or rugulose, at least above
5'Terminal inflorescence often exceeding 30 cm, massive; tepals of female flowers unequal, the inner shorter than the outer; utricle smooth or rugulose
6Bracts usually 3.5 mm or longer, definitely exceeding the tepals; seeds reddish-brown or black
6'Bracts shorter than 3.5 mm, shorter than the tepals; seeds white, tawny, reddish-brown or black