Succulent perennial of the Crassulaceae family, this cultivar is selected from Sempervivum calcareum, a species endemic to the limestone Alps of Southwestern France. The name 'Nigrans' is of old horticultural use; it should be noted that its formal registration as a cultivar could not be verified with certainty in the sources consulted, but it has long circulated in specialized collections.
Compared to the type species, 'Nigrans' is distinguished by a very pronounced dark coloration of the central and upper parts of the leaves, which turn dark purple-brown, almost black in the sunniest conditions, while the base of the leaves retains a deep and bright green. This contrast between the deep green of the outer leaves and the dark heart of the rosettes is the most striking feature of this cultivar. The rosettes, of medium to large size, are well open and geometrically regular. A finely ciliated light border highlights the edge of the leaves, a detail visible on adult rosettes.
The flowering, pale pink, is borne on stems 15 to 20 cm tall. In its natural habitat, the flowering of the type species extends from June to August; in cultivation, this cultivar generally flowers in June-July.
Same requirements as the type species: full sun, well-drained substrate preferably limestone, well-tolerated summer drought, total hardiness.