Question: what is the plural of Sempervivum? Anyway, the houseleeks all form tight rosettes of fleshy leaves, each rosette producing a number of offsets each year, so that a spreading, tight mat soon forms. After a few years a rosette may decide to flower, in which case it sends up a short stem, topped with a cluster of flowers, pink or yellow. It then dies, its place in the mat taken by youngsters. There are hundreds of named varieties, of which we offer some of the more distinctive ones, including some new varieties, bred by the late Matthew Ruane at Brynhyfryd Nursery. See also Jovibarba.

Sempervivum marmoreum subsp. reginae-amaliae has open rosettes of lime-green leaves, tinged red at the tips. The clusters of flowers in summer are red. It comes from Greece, where it grows in crevices in limestone rocks.