| 1 | Flower-bearing areoles and pericarpel deeply sunken into the stem, areoles with dense tufts of bristles and wool |
| 1' | Flower-bearing areoles not deeply sunken, areoles not densely woolly |
| 2 | flowers white |
| 2' | flowers coloured (orange, pink, magenta) |
| 3 | Flowers 3–4 cm long, receptacle-tube well developed |
| 3' | Flowers smaller, receptacle-tube not developed |
