2. RHODODENDRON L.
Trees or shrubs, with scaly bark, terete branchlets, terminal buds formed in summer, and fibrous roots. Leaves usually clustered at the end of the branches, revolute and entire on the margin, persistent or deciduous. Flowers in terminal umbellate corymbs from buds with numerous caducous scales; calyx 5-parted or toothed, persistent under the fruit, corolla 5—10-lobed, deciduous; stamens 5 or 10, rarely more, more or less unequal, ultimately spreading; filaments subulate-filiform, pilose at the base; disk thick and fleshy, crenately lobed; ovary 5—10-celled; style slender, crowned with a capitate stigma and persistent on the fruit; ovules numerous in each cell, attached in many series to an axile 2-lipped placenta projected from the inner angle of the cell, anatropous. Fruit a woody many-seeded capsule. Seed scobiform; seed-coat loose, reticulate, produced at the ends beyond the nucleus into a short often laciniate appendage; embryo minute, cylindric, axile in fleshy albumen; cotyledons oblong, shorter than the radicle turned toward the hilum.
Rhododendron with some four or five hundred species occurs in eastern Thibet, on the Himalayas, in southwestern China, the Malay peninsula and Archipelago, New Guinea, northern China and Corea, Japan, the mountains of central Europe, on the Caucasus, and in eastern and western North America, the largest number of species being found in southwestern China and on the Himalayas. Of the twenty-three or twenty-four North American species one only is arborescent.
Rhododendron possesses astringent narcotic properties. It produces hard close-grained compact wood sometimes used in turnery and for fuel. Many of the species are cultivated in gardens for the beauty of their large and conspicuous flowers.
The generic name is from ῥόδον and δένδρον, the Rose-tree.
1. [Rhododendron maximum] L. Great Laurel. Rose Bay.
Leaves revolute in the bud, ovate-lanceolate or obovate-lanceolate, acute or short-pointed at apex, and narrowed, cuneate or rounded at base, when they unfold covered with a thick pale or ferrugineous tomentum of gland-tipped hairs, and at maturity glabrous, thick and coriaceous, dark green and lustrous on the upper surface, usually pale or whitish on the lower surface, 4′—12′ long and 1½′—2½′ wide, with a broad pale midrib and obscure reticulate veinlets; persistent for two or three years; petioles stout, ridged above, rounded below, 1′—1½′ in length. Flowers: inflorescence-buds surrounded at first by several loose narrow leaf-like scales, and when fully grown in September cone-shaped, 1½′ long and ½′ broad, with many imbricated ovate scales rounded and contracted at apex into a long slender point, opening late in June after the shoots of the year from buds in the axils of upper leaves have reached their full length; flowers on slender pink pedicels covered with glandular white hairs and furnished at base with two linear scarious bractlets, from the axils of the scales of the inner ranks of the inflorescence-bud, in 16—24-flowered umbellate clusters 4′—5′ in diameter, with accrescent scarious resinous puberulous bracts, those of the outer ranks becoming 1′ long and ⅓′ wide, and shorter than the lanceolate bracts of the inner ranks contracted into a long slender point; calyx light green and puberulous, with rounded remote lobes; corolla prominently 5-angled or ridged in the bud, campanulate, gibbous on the posterior side, puberulous in the throat, light rose color, purplish, or white, 1′ long, cleft to the middle into 5 oval rounded lobes, with conspicuous central veins, the upper lobe marked on the inner face by a cluster of yellow-green spots, and furnished on the outer surface at the bottom of each sinus with a conspicuous dark red gland; stamens 8—12, white, inserted on the bright green disk; filaments enlarged and flattened at base, slightly bent inward above the middle, and bearded with stiff white hairs, the 4 or 5 short ones at the back of the flower for more than half their length and the others only near the base; ovary ovoid, green, coated with short glandular pale hairs, crowned with a long slender glabrous white declining style club-shaped and inflexed at apex, and terminating in a 5-rayed scarlet stigma. Fruit dark red-brown, ovoid, ½′ long, glandular-hispid, ripening and shedding its seeds in the autumn, the clusters of open capsules remaining on the branches until the following summer; seeds oblong, flattened, the coat prolonged at the ends into scarious fringed appendages.
A bushy tree, 30°—40° high, with a short crooked often prostrate trunk occasionally 10′—12′ in diameter, stout contorted branches forming a round head, and branchlets green tinged with red and covered with dark red or slightly ferrugineous glandular-hispid hairs when they first appear, dark green and glabrous in their first winter, gradually turning bright red-brown in their second year, and ultimately gray tinged with red, the thin bark separating on branches four or five years old into persistent scales; more often a broad shrub, with many divergent twisted stems 10°—12° high. Winter-buds: leaf-buds conic, dark green, axillary, or terminal on barren shoots, with many closely imbricated scales, those of the inner ranks accrescent, increasing in length from the outer to the inner, and at maturity 1½′ long, ¼′ wide, gradually narrowed at base, and terminating at apex in a long slender point, light green, glabrous, closely held against the shoot by a resinous exudation from the glandular hairs, and in falling marking the branchlet with numerous conspicuous narrow remote scars persistent for three or four years. Bark of the trunk about 1/16′ thick, light red-brown, broken on the surface into small thin appressed scales. Wood heavy, hard, strong, rather brittle, close-grained, light clear brown, with thin lighter colored sapwood; occasionally made into the handles of tools and used as a substitute for boxwood in engraving. A decoction of the leaves is occasionally employed in domestic practice in the treatment of rheumatism.
Distribution. Nova Scotia, Mt. Chocorua, New Hampshire, and southward in New England and eastern New York and along the Appalachian Mountains to northern Georgia and westward to the northern shores of Lake Erie and to southeastern Ohio (Hocking and Fairfield Counties); rare at the north and an inhabitant of deep cold swamps in a few isolated stations; more abundant on the mountains of western Pennsylvania, becoming exceedingly common farther south and occupying the steep banks of streams up to altitudes of 3000°; of its largest size on the high mountains of eastern Tennessee and the Carolinas, and here often forming thickets hundreds of acres in extent.
Often cultivated as an ornament of parks and gardens in the United States, and in Europe, and one of the parents of a number of distinct and beautiful hybrids.