An evergreen shrub of the same habit as R. ferrugineum, 2 to 3 ft high; young shoots bristly and scaly. Leaves narrowly oval, occasionally somewhat obovate or lanceolate, about 1 in. long, 1⁄4 to 1⁄2 in. wide, bright green above, somewhat scaly beneath, the margins crenulate, fringed with bristles. Flowers rosy pink to rosy scarlet, 1⁄2 in. to 3⁄4 in. across, produced in June in terminal clusters. Calyx and flower-stalk bristly and scaly, the latter 1⁄2 to 1 in. long. Corolla slightly scaly outside, funnel-shaped at the base, the lobes spreading. Bot. Mag., t. 1853. (s. Ferrugineum)
Native of the central and eastern Alps and of N.W. Yugoslavia; cultivated by John Tradescant 1656. This species although palpably a close ally of R. ferrugineum, and having the same popular name, is in several respects very distinct. The bristly character of the leaves, shoots, and calyx to which the specific name refers is, of course, its most distinctive feature, but it differs also in being greener and less scaly underneath the leaf, and in the usually longer calyx-lobes and flower-stalk.
In the wild, R. hirsutum is usually found on a limestone formation, but its soil preferences are not so definite as those of R. ferrugineum, which is never found on limestone except where the soil is so leached as to be slightly acid or unless there is an accumulation of peat above the substrate, whereas R. hirsutum, despite its preference for calcareous soils, can and does grow on slightly acid soils. Where the two species are contiguous, R. hirsutum is confined to dry, open, stony soils and screes, while R. ferrugineum prefers damper and shadier locations, with a soil richer in humus. A further difference is that R. hirsutum is a less gregarious species, rarely forming extensive pure stands as its ally so often does (Hegi, Fl. Mitteleuropa, Vol. V.3, p. 1639).
f. albiflorum Goiran – Flowers white. According to Schroeter it is less common in the wild than the white-flowered R. ferrugineum. 'Albiflorum Laciniatum' is a curiosity which arose in cultivation on a white-flowered plant and was grown by Froebel of Zurich; the leaves at the base are quite deeply incised (Schroeter, Pflanzenleben der Alpen, p. 113).
f. latifolium (Hoppe) Zab. R. hirsutum var. latifolium Hoppe – Leaves broad, almost rounded (see Schroeter, op. cit., fig. 36).