Native of N.W. Yunnan and upper Burma at 8,000 to 12,000 ft altitude; discovered by the Abbé Delavay about 1885 in the Tali range, Yunnan. It was introduced by Forrest in 1906 and first flowered with E. J. P. Magor at Lamellen, Cornwall, in 1914.
This beautiful rhododendron may be regarded as the Yunnan representative of R. maddenii, a well-known Himalayan species long cultivated in greenhouses. Being much the hardier, it is a valuable acquisition. It has lived in the open air at Kew through a few mild winters and occasionally flowered, but it needs a milder climate. It flowers in June and, starting late into growth, escapes late spring frosts, which may account for its comparative hardiness. R. maddenii differs in having glabrous stamens and the calyx-lobes are only 1⁄6 in. long. Forrest has introduced a number of forms of R. crassum differing in the shape and size of the leaves, some of which have glabrous stamens. Award of Merit June 24, 1924, when shown by T. H. Lowinsky, Sunninghill, Berks.
This becomes R. maddenii subsp. crassum. See further in this supplement.