Sub-genus I
Sempervivum proper.
Parts of the flowers usually in twelves. Open flower bell-shaped. RHODANTHA.--Flowers reddish.
Group 1. Ciliata. Leaves of the barren rosette glabrous on the face when mature, shortly ciliated on the edges only. Leaves large, green or slightly glaucous, with a conspicuous, red-brown tip: S. arverncnse, S. Boissieri, S. Boutignyanum, S. calcaratum, S. tectorum. Leaves large, green or glaucous; red-brown tip none or very obscure: S. atlanticum, S. glaucum, S. Lamottei, S. Schottii. Leaves large, purplish-brown throughout: S. triste. Leaves large, very glaucous, with a distinct red-brown tip: S. calcareum. Leaves small, green, with a distinct red-brown tip: S. parvulum. Leaves small, glaucous, with a distinct red-brown tip: S. Greenii. Leaves small, green; red-brown tip none or very obscure: S. Funckii, S. Verloti.
Group 2. Pubescentia. Leaves of the barren rosette pubescent on the face, as well as ciliated on the edges, not tipped with a tuft of spreading hairs. Flower small; stamens two-thirds as long as the petals: S. assimile. Flower large; stamens half as long as the petals: S. anomalum, S. flagelliforme, S. montanum.
Group 3. Barbatula. Leaves of the barren rosette strongly ciliated on the edges, and furnished with a tuft of short, straight hairs at the tip. Moderately tall: S. Fauconneti, S. fimbriatum, S. Pomelii. Dwarf: S. barbatulum.
Group 4. Arachnoidea. Dwarf species, with the tips of the inner leaves of the rosette connected by fine, fleecy threads, like a spider's web. Arachnoid threads many: S. arachnoideum, S. Moggridgei. Arachnoid threads few: S. Doellianum, S. oligotrichum.
CHRYSANTHA.--Flowers yellow.
Leaves obovate-cuneate, glabrous on the face: S. Wulfeni. Leaves obovate-cuneate, hairy on the face: S. Braunii, S. grandiflorum, S. ruthenicum. Leaves oblanceolate, very hairy on the face: S. Pittoni.