| 1 | Sympodial growth with basitonic or mesotonic branching |
| 1' | Monopodial growth, simple stems, branches are produced only after an injury |
| 2 | Plants with basitone pattern of branching, lateral cephalium present |
| 2' | Plants with mesotone pattern of branching, variable degree of ramification, differentiated or undifferentiated flowering region |
| 3 | Undifferentiated flowering region |
| 3' | Flowering region differentiated in an apical pseudocephalium |
| 4 | High degree of ramification, slender plagiotropic branches, subapical flowering, floral tube pinkish |
| 4' | Low to moderate degree of ramification, orthotropic branches variable in thickness, flowering variable in position, floral tube green or often reddish |
| 5 | Low degree of ramification, often simple stems, subapical flowering, papyraceous scales on flowers and fruits |
| 5' | Moderate degree of ramification, apical to subapical flowering, fleshy scales on flowers and fruits when present |
| 6 | Thin branches (<12 cm diam.), 25 ribs or more, reddish to brownish spines concentrated towards the stem apices, floral tube dark red colored |
| 6' | Thick stem and branches (>20 cm diam), stems with less than 17 ribs, stem apices densely covered with trichomes or spines, floral tube green or reddish |
| 7 | Reproductive stem apices covered with brownish trichomes, podaria evident near the apex, apical flowering |
| 7' | Whitish to reddish spines concentrated towards the apex, podaria not evident, subapical flowering |
| 8 | Permanent yellowish apical pseudocephalium, thick stems (> 20 cm diam), red flowers densely covered with trichomes and bristles, lime-green stems |
| 8' | Intermittent apical pseudocephalium leaving annular remnants from flowering events, thin stems (<15 cm diam), green bare flowers, green to dark green stems |
| 9 | Tall plants, from 3 to 5 m in height, few branches (up to 5), often simple stems (up to 12 cm diam), 24 to 28 ribs |
| 9' | Short plants, up to 2 m in height, with more than five branches |
| 10 | Few branches (5 to 10), 8 to 10 cm diam., 24 to 26 ribs |
| 10' | Several branches (up to 20), up to 8 cm diam., 21 to 23 ribs |
| 11 | Differentiated flowering region in a lateral cephalium |
| 11' | Undifferentiated flowering region |
| 12 | Flowering along the stem, less than 20 ribs, 5 to 7 radial spines in stem areoles |
| 12' | Flowering concentrated below subapical region but can emerge scarcely along the stem, pinkish internal tepals, up to 20 ribs |
| 13 | Thick stems up to 15 m height, 60 cm diam., up to 16 ribs, floral tube green |
| 13' | Thin stems up to 7 m height, 12 cm diam, up to 20 ribs, floral tube reddish green |
| 14 | Numerous ribs (up to 40), thick stem up to 40 cm diam, flower up to 6 cm in length, spines yellow, 7 to 9 radial spines in stem areoles |
| 14' | Few (8 to 10) prominent ribs, thin stem up to 12 cm diam, flower up to 10 cm in length, spines white to grey, 3 radial spines in stem areoles |
