1	"Upper surface of petals yellow or yellow-green, at least towards the tip"	2
1	"Upper surface of petals white, red, pink or purple"	3
2	"Rosettes mostly open; plant with resinous odour and sticky leaves; petals 12–20 mm long, 2 mm wide"	"Sempervivum montanum"
2	"Rosettes usually wholly or partly closed; plant without a resinous odour and the leaves not sticky; petals 10–12 mm long, 1.5 mm wide"	"Sempervivum ciliosum"
3	"Mature leaves hairless except for marginal cilia (rarely a few scattered hairs)"	"Sempervivum tectorum"
3	"Mature leaves hairy on both surfaces"	4
4	"Apical cilia of leaves long and flexuous, interwoven to form a web-like covering"	"Sempervivum arachnoideum"
4	"Apical cilia short, not web-like"	5
5	"Plant with resinous smell and sticky leaves; cilia of rosette leaves scarcely longer than other hairs"	"Sempervivum montanum"
5	"Plants without resinous smell and sticky leaves"	6
6	"Petals with white margins"	"Sempervivum kosaninii"
6	"Petals without white margins"	7
7	"Rosette symmetric; few offsets produced on stout, stiff stolons to 5 cm long; leaves dark green with reddish purple apices; petals 9–10 mm long, deep red"	"Sempervivum cantabricum"
7	"Rosette often asymmetric; numerous offsets produced on very short, slender stolons that soon wither; leaves pale green and apices not coloured; petals about 15 mm long, pale pink or pink with a darker median band"	"Sempervivum atlanticum"