Astrophytum Artenschlüssel / key to the species
BACKEBERG, C. 1937 . Blätter f. Kakteenforschung Astrophytum LEM. (1839)

A) Fruits splitting like a star, flower throat yellow
a) Flowers large, body usually 5-angled....................................Astr. myriostigma Lem.
b) Flowers smaller, body 4-angled............................................Astr. myriostigma subsp. quadricostatum
c) Flowers smaller, body 5-angled, whitish..............................Astr. myriostigma subsp. tulense hort? (Möll.)
.....also: v. nuda R. Mey. and v. columnaris K. Sch.
d) Body becoming cylindrical, spines hard, brown..................Astr. ornatum Web.
.....v. glabrescens Web. is almost green. v. Mirbellii K. Sch. has golden spines

B) Fruits not splitting like a star or bursting at the base, flowers red-throated
a) Body 4-angled, chal white, fruit purple red........................Astr. coahuilense (Möll.) Bckbg.
...(note from Heinz Hoock: the body is 5-angled as Backeberg writes it correctly in the German text, but in the English version occured this error)
b) Body with elastic spines......................................................Astr. capricorne Br. & R.
....also: v. crassispinum Möll. and minor R. & Quehl. but hardly justifiable though:
c) Body chalk white, spines weak, black.................................Astr. capricorne v. niveum Kays.
d) Body pure green, spines weak, flecked with brown...........Astr. senile Fric.
e) Body pure green, spines weak, yellow...............................Astr. senile v. aureum Möll.
f) Body flat, fruit greyish-red..................................................Astr. asterias Lem.

The very difficult Astr. coahuilense comes between A. and B.