A low, spreading, much-branched shrub up to 18 in. high, the stems and leaves thickly clothed above and below with a close, white, stellate down, giving the whole plant a mealy appearance. Leaves linear-oblong or linear, the margins much recurved, 1⁄2 to 1 in. long, 1⁄8 to 1⁄5 in. wide, bluntish or pointed; stipules linear. Cymes terminal, producing numerous flowers in succession. Flowers pure white, 1 in. or rather more across, nodding in the bud state, but becoming erect at expansion. Petals obovate, slightly toothed at the end. Sepals five, the two outer ones linear, very small; the three inner ones ovate, twice as long as the others, all white with down.
Native of S. and W. Europe (and of N. Africa), but absent from the Alps proper and not extending far eastward into Germany. It is a rare native of Britain, found always on limestone, on Brean Down in Somerset and Berry Head in Devon. It was introduced to gardens before 1768, at which time Miller had plants from various sources, though not from the English stands, of which he was probably unaware. H. appeninum is slightly variable in its foliage, the leaves being sometimes green above, or more or less plane. But in the allied H. nummularium the leaves are invariably green above and never more than slightly revolute; and the flowers commonly yellow or orange-yellow. The key-character by which botanists distinguish the two species is: stipules linear in H. appeninum, equalling or slightly longer than the petioles; stipules lanceolate or linear-lanceolate, leaflike and always longer than the petioles in H. nummularium.
H. appeninum (and its var. roseum) is one of the parents of the garden hybrids.
var. roseum (Jacq.) Schneid. Cistus roseus Jacq.; H. rhodanthum Dun.; H. appeninum var. rhodanthum (Dun.) Bean; H. rhodanthum var. carneum Dun. – Flowers pink. Leaves green and almost glabrous above. Found wild in N.W. Italy (Liguria and Piemonte) and in the Balearic Islands. The garden variety called ‘Rhodanthe Carneum’ is a hybrid and not, as might be supposed from the synonym given above, a form of H. appeninum var. roseum.
H. × sulphureum Willd. – Here belong hybrids between H. appeninum and H. nummularium, which occur quite commonly where the two species are in contact. Flowers pale yellow. Leaves narrow-lanceolate, green and stellate-hairy above. In gardens, hybrids between H. appeninum var. roseum and H. nummularium were in cultivation early in the 19th century, and of the plants figured by Sweet in his Cistineae two are considered to be of this parentage (t. 51 as H. canescens and t. 66 as H. cupreum).