An evergreen shrub or a tree up to 35 ft high, the young shoots silvery grey, very stout, and up to 1 in. thick. Leaves oval or oblong, occasionally obovate, rounded at both ends, ordinarily 10 to 20 in. long, 6 to 12 in. wide, at first grey scurfy above, ultimately dark green and glabrous, silvery grey beneath with a closely appressed scurf, not downy or hairy in the ordinary sense of those words; midrib very prominent beneath as are also the fourteen to sixteen pairs of roughly parallel veins springing from it; stalk very stout (up to 1⁄2 in. thick) 1 to 2 in. long. Flowers produced in April in a racemose truss of twenty to thirty, and about 9 in. wide; pedicels about 11⁄2 in. long, densely woolly. Calyx woolly, fringed with small teeth. Corolla bell-shaped, fleshy, dull creamy white to soft yellow, marked with red patches at the base, 2 in wide, eight- to ten-lobed, the lobes 3⁄4 in wide, notched. Stamens eighteen or twenty, downy towards the base, shorter than the corolla. Ovary covered with reddish down; style glabrous; stigma 2⁄5 in. wide. Bot. Mag., t. 8973. (s. Grande)
R. sinogrande was discovered by Forrest in 1912, growing at 11,000 ft on the western flank of the Shweli-Salween divide, latitude 250 20′ N. The plants were in fruit and from them the species was introduced to gardens (F.9021). In this area, on the borders between Burma and mid-Yunnan, R. sinogrande is at the south-eastern extremity of its area. From here it ranges along the mountains between the Salween and the eastern branch of the Irrawaddy to some way north of 28° and is also found east of the Salween in this latitude. Most of Forrest's later sendings are from this northeastern corner, where Burma, China and Tibet adjoin. Westward it ranges across the upper Irrawaddy to the Delei valley in the Mishmi Hills, Assam, but its western limit is uncertain.
'R. sinogrande sometimes forms forests single-handed. We passed through whole glades of its gnarled and twisted branches, when its pale yellow globes were alight and shining brighdy under the dark canopy of leaves. Some of the trunks were twenty-four inches round. . . . One advantage about R. sinogrande is the lateness of its new growth. The great spear-headed buds burst in July, and even in August one can pick out the trees a mile away by the plumes of silver foliage shooting up from ruby-red tubes' (Kingdon Ward, Plant Hunting on the Edge of the World, p. 277, in reference to R. sinogrande in the Mishmi Hills).
Botanically this is the eastern counterpart of R. grande, differing in the eglandular ovary and pedicels and the shorter and stouter style. In leaf it is much the finer species and in that respect the most splendid and remarkable of all rhododendrons, or indeed of all woody plants hardy in this country. In the Cornish woods, where it first faced the English climate, leaves 21⁄2 ft long and 1 ft or more wide have been produced on young plants. It first flowered at Heligan in Cornwall in May 1919. It grows fastest and has attained the largest size in the Atlantic zone, but in woodland gardens south of London it is perfectly at home and flowers just as well as in the milder parts. It is nearly hardy and in some forms completely so. In the Windsor collection some plants were cut to the ground by the freezing winds of February 1956, but others were unharmed or almost so, and none was actually killed (R.C.Y.B. 1957, p. 62).
R. sinogrande was awarded a First Class Certificate when shown by G. H. Johnstone, Trewithen, Cornwall, on March 9, 1926. Four years earlier, Dame Alice Godman had shown a truss from a plant grown under glass at South Lodge, Sussex, and the species had then received an Award of Merit as a tender rhododendron. The plant was a gift from J. C. Williams of Caerhays and also provided the truss figured in the Botanical Magazine.
var. boreale Tagg & Forr. – Described as having rather more leathery and smaller leaves than in the type and flowers soft yellow throughout without markings or pale yellow with a crimson blotch at the base. Introduced by Forrest in 1922 (F.21750). It is sometimes referred to as the 'northern form' of R. sinogrande (it was collected in latitude 28° 18′ N.), but Forrest's 20387, introduced the previous year, came from still farther north and is not mentioned in the description of var. boreale.
From the Supplement (Vol. V)
The var. boreale is not recognised in the Edinburgh revision.