Forms spreading mats of silvery encrusted rosettes of linear-spathulate leaves, thickened and recurved at the tips and varying considerably in both length and width according to locality of occurrence. Botanically two subspecies have been made, subsp. callosa from the Alps and Apennines, leaves 2.5-9cm long and 2.5-6mm wide and subsp. catalaunica from north-eastern Spain and southern France with leaves 1.5-3cm long and 4-6mm wide. Within this geographical range, forms between these extremes have been collected and given varietal names. The following are most often encountered in horticultural literature: 'Albertii'; a large and spreading form which is probably a hybrid with S. cotyledon or S. longifolia. Var. australis; a fine form occurring in central and southern Italy with leaves up to 8cm long and 5-9mm at the tip, narrowing below. Produces 30cm long, low arching and densely flowered one-sided wands of pure white flowers. Var. lantoscana; a fine form from the Maritime Alps botanically now amalgamated with var. australis but tending to have shorter, blunter, spathulate leaves and good inflorescences 20-25cm long. Var. billardii; a form from the south-western Alps and northern Apennines with long, narrow hairless leaves and smooth inflorescences up to 50cm long. This is the typical northern form of the taxonomists' subsp. callosa of which var. australis is the typical southern form.