Rhododendron (Gr. , rose tree, the ancient name), a genus of plants of the order ericaceae or heath family, to which the name rose bay has been given, but the botanical name is in more common use. The rhododendrons are shrubs or low trees with evergreen, entire, alternate leaves, and (usually) large showy flowers in close terminal clusters, from large scaly-bracted buds. The bell-shaped or funnel-shaped corolla is five-lobed, and often somewhat irregular; the ten stamens (rarely less) are usually declined or bent downward, as is the elongated style; anthers short, opening by terminal pores; pod five-celled, five-valved, and many-seeded. The genus is widely distributed, some species occurring in the arctic zone, others in the temperate portions of North America, still others in Europe and China, while in the mountains of India they are very numerous. Four species are found east of the Mississippi, one of which, the Lapland rhododendron (R. Lapponicum), belongs to the arctic flora of both continents, and with us is found only on the alpine summits of the mountains of Maine, New Hampshire, and New York; it is a little, dwarf, prostrate species, with branches only a few inches long, its stems and leaves dotted with rusty scales; the flowers are open, bell-shaped, violet purple and dotted.
The great rhododendron (R. maximum), also called great laurel, is found sparingly from Maine to Ohio, but is very common in the mountains of the middle states, and along the watercourses as far south as Georgia; it flourishes best in deep, damp woods, and in cedar swamps it often forms the principal undergrowth. It is from 6 to 20 ft. high, with the habit of a shrub rather than of a tree. The leaves are very thick and leathery, from 4 to 10 in. long, elliptical-oblong, acute, narrowed toward the base, somewhat revolute or turned over on the margins, very smooth, and dark green. The flowers appear in July in large clusters, with somewhat viscid stalks; the corolla is an inch broad, white or pale rose-colored, and greenish at the throat on the upper side and spotted with yellow or reddish dots; a variety is sometimes met with having pure white and one with purplish flowers. This species is not common in cultivation, and succeeds best in a shaded situation; some hybrids have been produced from it, but very few in number compared with those from the next.
The Catawba rhododendron (R. Catawbiense) grows on the higher Alleghanies from Virginia to Georgia. It is a compact shrub, from 3 to 6 ft. high; its oval or oblong leaves are rounded at both ends, pale beneath, and 3 to 5 in. long; the broadly bell-shaped flowers are lilac purple, and on (usually) rusty-downy stalks. This species, hybridized with tender exotic species, is the original of the fine ornamental rhododendrons to be mentioned presently. The dotted rhododendron (R. punctatum) completes the list of the eastern native species; this is found from the mountains of North Carolina southward, a small-leaved form occurring in West Florida. It grows 4 to 6 ft. high, has leaves 2 to 4 in. long, and, though evergreen, thinner than in the other species, and their lower surface, as well as branchlets, and outside of the flowers, sprinkled with rusty dots; the flowers are rather small and rose-colored. - Two species, both first described and figured by Sir William Hooker, occur in the far west. The white-flowered rhododendron (R. albiflorum), first found on the Rocky mountains, and since on the Cascade range, is a low shrub with drooping cream-colored flowers, unlike those of others in appearance.
The Californian species (R. Californicum), from the mountains of California, has proved hardy in England, and is described as of moderate size, good habit, and having very showy rose-colored flowers. - The most important exotic species is the Pontic rhododendron (R. Ponticum), from Pontus in Asia Minor; it is sometimes 20 ft. high, but usually less than half that height. Its obovate-lanceolate leaves taper to the base, and its large, very open bell-shaped corolla is purple, opening in early spring. This is the common rhododendron of European gardens, and, though not generally hardy in our northern states, sometimes succeeds if kept as a low bush and given a slight protection, without which its flower-buds will be winter-killed. Its chief use in this country is to furnish stocks upon which to graft hardier kinds, as it grows readily from seeds. In Europe it has produced a number of varieties, some of which are hardier than the species. The tree rhododendron (R. arboreum) is a noble species from Nepaul, and still more tender than the Pontic; the dark green leaves are silvery white beneath, and the large clusters of flowers are scarlet, varying, even in the wild state, through various shades to pure white.
The catalogue of varieties is a long one, but they can only be cultivated in the northern states, as in England, under glass, where, when room can be afforded, they make a most brilliant show. Other exotic species seen in rare collections are the yellow-flowered (R. chrysanthum), from the Caucasus; the hairy (R. hirsutum), very dwarf, with pale red flowers; and the Daurian (R. Dauricum), from Siberia, a dwarf species with bright rose-purple and very early flowers; these three are hardy. A magnificent group of rhododendrons is found in the Himalaya, presenting a great variety in foliage and flowers, as well as habit of growth, some of them being epiphytes; they require to be cultivated under glass, both here and in Europe; the majority of these were first made known by Dr. J. D. Hooker, to whose work, "The Rhododendrons of the Sikkim Himalaya," reference may be made for descriptions and colored plates of these wonderfully beautiful plants. - The rhododendrons of our gardens are known as hybrids of R. Catawbiense; European horticulturists have long practised hybridizing this species with R. arboreum, R. Ponticum, and possibly others; among these hybrids are many very beautiful varieties which do not endure northern winters, requiring to be housed; but there are several perfectly hardy varieties, which some experienced cultivators think are not hybrids at all, but merely seedling variations of R. Catawbiense. Especial attention is given to these plants in England, and their popularity in this country is increasing.
For beauty of form and foliage and profusion and variety in flowers no other shrubs can equal them. Their general cultivation has been hindered by the supposition that they require a peat soil; but the plants, at least those raised in this country, will flourish perfectly well in any good garden soil that is not calcareous; they will not succeed in a heavy clay or on a limestone soil. The varieties are numbered by hundreds; twelve well tested sorts are: grandiflorum, album elegans, roseum elegans, Everestianum, album grandiflorum, giganteum, Lee's dark purple, gloriosum, macranthum, purpureum elegans, candidissimum, and speciosum. The rhododendrons are exceedingly manageable plants; they may be taken up at almost any time without injury, and when in full bloom may be lifted and used for the decoration of rooms, and set out again without showing the effects of the disturbance. In England the commoner seedlings are largely planted to form game coverts. - But little positive is known about the active properties of our native rhododendrons; narcotic powers are attributed to R. maximum, while others regard it as a simple astringent; Michaux says that R. punctatum yields a honey that is deleterious, but this statement needs confirmation.
The information in regard to exotic species is hardly more definite; the yellow-flowered rhododendron is said to be narcotic and dangerous. In India the natives eat the flowers of R. arboreum, and European residents prepare a conserve from them; this species secretes honey in such quantities that when the bush is shaken it falls like rain in large drops.
Hybrid of Rhododendron Catawbiense.