1A.	Leaflets 1.2–2 cm long or longer	A. tequilana ssp. tequilana
1B.	Leaflets 1 cm long or shorter	2
2A.	Herbaceous, perennial, commonly prostrate	A. hartwegii
2B.	Shrubs or small trees	3
3A.	Leaflets with reticulate or brochidodromous venation or pinnately veined	A. lemmonii
3B.	Leaflets with only 1 vein, prominent or barely visibly	4
4A.	Leaflets with inconspicuous reticulate venation or sometimes withonly the midrib	A. lemmonii
4B.	Leaflets with conspicuous reticulate venation	A. hartwegii
4A.	Stems and foliage glabrescent; leaflets short ciliate or glabrous; pinnae 6 pairs per leaf or fewer (rarely 8 pairs)	A. angustissima ssp. texensis
4B.	Stems and foliage glabrous or pubescent; pinnae 7 or more pairs per leaf	5
5A.	Branches, petiole, and leaf rachis glabrous or pulverulent, the trichomes white, appressed; pinnae 11–17 pairs per leaf; calyx glabrous; pod long beaked	A. angustissima ssp. angustissima
5B.	Branches, petiole, and leaf rachis densely hispidulous or pilose, the trichomes yellow, erect; pinnae 18 or more pairs per leaf; calyx hirustuluos; pod abruptly rounded apically	A. angustissima ssp. filicioides