A deciduous shrub of bushy habit eventually 6 to 8 ft high, with twiggy branches, hairy when young. Leaves thinly arranged along the shoot or in a tuft of five or six at the end, obovate, 1 to 2 in. long, tapering to a short stalk at the base; dark green and glabrous above, paler and bristly along the midrib beneath; margins bristly. Flowers produced during June and July at the end of the previous year's shoots, six to twelve together in a cluster. Calyx small, and like the slender flower-stalk, glandular-hairy. 3⁄4 in. long, curved, hairy. Corolla white or pink, 1 to 11⁄4 in. long, the lower half is a narrow tube often more highly coloured, the upper half five expanded oblong lobes 3⁄4 in. long. The whole corolla, but especially the tubular part, is covered with sticky hairs. Stamens exserted. Ovary clad with usually gland-tipped bristles; style longer than the stamens, downy in the lower part. (s. Azalea ss. Luteum)
Native of eastern N. America; introduced in 1734, and still one of the most delightful of garden shrubs because of its late blossoming and its exquisitely fragrant flowers. It is the reputed parent, or one of the parents of a great number of garden azaleas. Loddiges in their catalogue for 1836 gave a list of one hundred and seven varieties, which, according to Loudon, were hybrids or varieties of R. viscosum. The identity of many of these old varieties is lost, but some are still to be obtained under their old names. Relatively few, however, show any viscosum 'blood', but rather that of R. periclymenoides and R. calendulaceum. The viscosum group at the present time is, as a matter of fact, a rather limited one, but is well distinguished by the lateness in flowering, strong fragrance, and the viscous blossoms.
var. glaucum (Ait.) Torr. Azalea viscosa var. glauca Ait. – The swamp honeysuckle is variable in the wild, more especially in the colour of the flowers and leaves. This is its most distinct variety, with pure white, fragrant flowers, and leaves blue-white on the lower, or sometimes on both, surfaces. A very charming shrub, flowering late like the type.
Other variants are described by Rehder in A Monograph of Azaleas, pp. 160-5. On the variability of R. viscosum Dr Henry Skinner writes: 'From the dwarf, twiggy and semi-evergreen bushes of the marshes of South Carolina to the tall, grey-leaved and large-flowered shrubs of the pond margins of Cape Cod, the Swamp azalea is much more changeable than its sister of the Gulf coast [R. serrulatum]. . . . It seems certain that not a little of the trouble is due to R. viscosum and arborescens having met on occasion in the northern states. . . . In some of these northern swamps genes have been so freely exchanged between these two species that nomenclatural assignment of present populations becomes virtually impossible' (R.C.Y.B. 1957, p. 28).
R. serrulatum (Small) Millais Azalea serrulata Small – Closely related to R. viscosum, which it replaces from mid-Georgia south to Florida and west to south-eastern Louisiana. According to Rehder its distinguishing characters are the red-brown branchlets, the leaves of firmer texture, finely but distinctly serrated at the margin, and the longer corolla-tube (about twice as long as the lobes, against one-and-a-half times as long in R. viscosum). It is remarkable for flowering very late in its natural habitat, but is of no importance for British gardens.