1	"Areoles narrowed, elliptic to more or less linear"	2
1	"Areoles rounded, round to oval "	5
2	"Flowers purplish magenta "	3
2	"Flowers yellow or bicolored; spines all radial, less than 4 mm long "	4
3	"Central spines 2–4 or more, radial spines mostly 14–18, comb-like "	"Rebutia mentosa"
3	"As above but contrast of red-brown central spines and white radials "	"Rebutia tiraquensis"
4	"Flowers yellow; spines stiff, 14–16 "	"Rebutia arenacea"
4	"Flowers purple with a white throat; spines up to 11 "	"Rebutia rauschii"
5	"Scales of flower tube with axillary hairs and/or bristles "	6
5	"Scales of flower tube more or less hairless, bristles absent "	11
6	"Flowers white or pale pink "	"Rebutia albiflora"
6	"Flowers orange or red "	7
7	"Spines short, comb-like flattened down "	"Rebutia heliosa"
7	"Spines bristly, not flattened down "	8
8	"Spines 30–40, 5–30 mm long "	"Rebutia fiebrigii"
8	"Spines less than 20, 3–5 mm long "	9
9	"Stems purplish "	"Rebutia kupperiana"
9	"Stems green "	10
10	"Ribs pronounced; flowers dark red "	"Rebutia spegazziniana"
10	"Ribs not pronounced; flowers red, orange or purple "	"Rebutia deminuta"
11	"Flower tube solid at the base, flowers yellowish "	"Rebutia marsoneri"
11	"Flower tube hollow, flower colour variable "	12
12	"Spines 2–4 mm long "	"Rebutia minuscula"
12	"Spines to 3 cm long "	"Rebutia senilis"