Shrubs or trees, to 3.5(-6) m, sometimes rhizomatous. Stems: bark smooth to vertically furrowed, shredding; twigs multicellular eglandular-hairy (hairs branched basally, crisp/matted), glabrate in age. Leaves persistent; petiole multicellular-hairy (hairs ± branched), often glabrescent; blade elliptic to obovate or slightly ovate, (5-)6-12(-17) × (2.5-)3.5-6(-7.7) cm (length/width ratio 1.3-3.5), thick, coriaceous, margins entire, revolute to plane, glabrous or sparsely hairy along margins (hairs branched, ephemeral), apex rounded/mucronate to obtuse or acute, surfaces sparsely eglandular-hairy (hairs basally branched, crisped, quickly deciduous), abaxial surface minutely, obscurely papillose. Floral bud scales multicellular stipitate-glandular-hairy, eglandular-hairy (hairs basally branched, crisped), and unicellular-hairy (hairs short to elongate), margins eglandular-hairy (hairs branched). Inflorescences 12-20-flowered; bracts similar to bud scales. Pedicels 10-50 mm, sparsely to moderately multicellular eglandular-hairy (hairs ferruginous, branched, crisped), glabrate in age. Flowers opening after development of leaves (of flowering shoots), erect to horizontal, fragrant; calyx lobes 0.5-1.7 mm, glabrous or eglandular-hairy; corolla deep pink to purple, rarely white, usually with yellowish-green spots on upper lobe, campanulate, 27-50 mm, glabrous on outer surface, petals connate, lobes 15-30 mm, tube gradually expanding into lobes, 12-28 mm; stamens 10, included, ± unequal, 19-39 mm; (ovary multicellular eglandular-hairy). Capsules borne on erect pedicels, 10-23 × 3.5-7 mm, eglandular-hairy (hairs ferruginous, branched). Seeds without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, loose. 2n = 26. Flowering spring. Rocky slopes, ridges, and balds; 50-2000 m; Ala., Ga., Ky., N.C., S.C., Tenn., Va., W.Va. Large-flowered, large-leaved plants of Rhododendron catawbiense from eastern North Carolina have been named forma insularis Coker. Rare hybrids with R. maximum have been reported by A. E. Radford et al. (1968) (R. ×wellesleyanum Waterer ex Rehder); we have seen no specimens.
Shrub or small tree to 6 m; lvs leathery, evergreen, oval or elliptic, 5-15 cm, broadest near the middle, rounded to subacute at both ends, glabrous; fls lilac-purple, somewhat larger than in no. 1 [Rhododendron maximum L.] ; pedicels and ovary hirsutulous, not glandular; sep broadly triangular or semicircular, under 1 mm; fr 20-25 mm. Mt. woods; Va. to Ky., s. to Ga. and Ala. May, June.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.