Astrophytum Artenschlüssel / key to the species
MEGATA, M. 1944. page 35-36, Kyoto Imperial University, An Account of the Genus Astrophytum LEMAIRE in: Memoirs of the College of Agriculture, No. 56

1.1 Flower smaller, without the carmine or orange centre; fruits dry, splitting starlike; seeds 40-60, black
I. Section Austrastrophytum
2.1 Plant 8 ribbed, with spines; scales on flower-tube spiny......................................1. Astr. ornatum
2.2 Plant 4 or 5 ribbed, without spines; scale on flower-tube bristle..........................2. Astr. myriostigma

1.2 Flower large, with carmine or orange centre; fruit berrylike, bursting irregularly at the base; seeds 80-300, black or dark brown
II. Section Septentriastrophytum
2.1 Plant globular or cylindric; scale on flower-tube bristle
3.1 Plant mostly 5-ribbed, without spines, bearing chalk white hairy scales.............3. Astr. coahuilense
3.2 Plant 8-ribbed, with spines; seeds numerous 240-300.........................................4. Astr. capricorne
2.2 Plant flat, without spines; scales on flower-tube hairy.........................................5. Astr. asterias