1	"Plant glabrous except axillary tufts of hairs"	2
1	"Plant variously hairy"	7
2	"Spines 6"	"Sclerolaena calcarata"
2	"Spines 3, 4 or 5"	3
3	"Leaves flat, linear to narrowly oblong or elliptic"	"Sclerolaena muricata"
3	"Leaves terete to semi-terete, fleshy"	4
4	"Spines 3"	"Sclerolaena tricuspis"
4	"Spines 4–5 (1 or 2 much shorter than others and sometimes obscure)"	5
5	"Spines 4 or 5 (3 prominent, 1 or 2 shorter); limb pubescent, exserted beyond spine-bases for 1–2 mm"	"Sclerolaena intricata"
5	"Spines 4 (3 prominent, 1 shorter and often obscure); limb glabrous, not or barely exserted above spine-bases"	6
6	"2 of the 3 larger spines lateral in line, not curving around the branch, the third abaxial; stamens 3"	"Sclerolaena divaricata"
6	"The larger spines not in line laterally, 1 abaxial, 1 lateral, and 1 somewhat adaxial and curved around branch; stamens usually 5"	"Sclerolaena cuneata"
7	"Fruiting perianth hard, cup-shaped to subglobular with c. 11 short spines radiating from the truncate apex"	"Sclerolaena stelligera"
7	"Fruiting perianth not as above, with up to 6 spines"	8
8	"Spines 2"	9
8	"Spines 3–6"	15
9	"Fruiting perianth with prominently hollowed base; spines less than 3 mm long"	10
9	"Fruiting perianth not prominently hollowed at base; spines more than 4 mm long"	11
10	"Spines divergent, mostly c. 2 mm long"	"Sclerolaena diacantha"
10	"Spines erect and almost parallel, mostly 0.5–1 mm long"	"Sclerolaena uniflora"
11	"Fruiting perianth (except limb) glabrous; leaves glossy, with appressed, medifixed hairs"	"Sclerolaena decurrens"
11	"Fruiting perianth hairy; leaves with basifixed hairs"	12
12	"Stems remaining pubescent; spines 8–20 mm long, hairy for much of their length"	13
12	"Older stems becoming glabrous; spines less than 8 mm long, usually only hairy near base"	14
13	"Leaves remaining grey- or white-woolly with spreading, distinctly barbed or shortly branched hairs"	"Sclerolaena limbata"
13	"Leaves glabrescent, or if remaining hairy, hairs, appressed, simple, smooth to scabridulous"	"Sclerolaena bicornis"
14	"Spines divergent and ascending in different vertical planes; hairs copious on tube; limb barely exserted beyond base of spines"	"Sclerolaena obliquicuspis"
14	"Spines divergent, but ascending in same vertical plane; hairs sparse on tube; limb prominently exserted above base of spines"	"Sclerolaena patenticuspis"
15	"Spines 6 (if ever 5, then fruiting perianth more than 2 mm long)"	16
15	"Spines 3–5 (when 5, fruiting perianth less than 2 mm long)"	18
16	"Branches glabrous except for axillary hair tufts; fruit strongly 10-ribbed, produced at the base into 1 or 2 short spreading spurs, usually distinctly pink to red at maturity"	"Sclerolaena calcarata"
16	"Branches hairy between leaves; fruit not or only weakly ribbed, not produced into basal spurs, not or rarely reddish"	17
17	"Branches sparsely cottony; the 2 shorter, radicular spines unequal (1 sometimes suppressed)"	"Sclerolaena napiformis"
17	"Branches with short, appressed hairs; the 2 shorter, radicular spines subequal"	"Sclerolaena parviflora"
18	"Spines 5"	19
18	"Spines 3 or 4"	20
19	"Perianth densely woolly; longer spines 8–15 mm long"	"Sclerolaena birchii"
19	"Perianth glabrous to minutely woolly; longer spines 5–10 mm long"	"Sclerolaena muricata"
20	"Tube of fruiting perianth glabrous; hairs of leaves medifixed"	"Sclerolaena decurrens"
20	"Tube of fruiting perianth hairy; hairs basifixed"	21
21	"Tube of fruiting perianth turbinate, flattened"	"Sclerolaena lanicuspis"
21	"Tube of fruiting perianth cylindric or barrel-shaped"	"Sclerolaena ventricosa"