Sp. Pl. 1: 392. 1753 ,.
Shrubs or trees, to 10 m, sometimes rhizomatous. Stems: bark smooth to vertically furrowed, shredding; twigs multicellular stipitate-glandular-hairy and eglandular-hairy (hairs basally branched, crisped/matted), glabrate in age. Leaves persistent; petiole multicellular-hairy (hairs ± branched), often glabrescent; blade oblong to obovate or elliptic, (6–) 9–20 (–31) × (1.5–) 2–5 (–8) cm (length/width ratio 2.4–8), thick, coriaceous, margins entire, revolute to ± plane, glabrous or sparsely hairy (hairs branched), apex acuminate to sometimes acute, surfaces scattered stipitate-glandular-hairy and eglandular-hairy (hairs forming dense mat, basally branched, crisped, abaxially becoming sticky and matted, forming ± scaly or continuous, pale, shellaclike coating, smooth to slightly roughened, hairs ± deciduous adaxially). Floral bud-scales stipitate-glandular-hairy, eglandular-hairy (hairs ferruginous, crisped), and short unicellular-hairy abaxially, margins hairy (hairs branched, long-celled). Inflorescences 10–25-flowered; bracts similar to bud-scales. Pedicels 17–60 mm, multicellular stipitate-glandular-hairy. Flowers opening after development of leaves (of flowering shoots), erect to horizontal, not or only slightly fragrant; calyx lobes 2–6 mm, stipitate-glandular-hairy; corolla white to pink, rarely deep pink to purple, with yellowish green spots on upper lobe, campanulate, 20–36 mm, scattered stipitate-glandular-hairy on outer surface, petals connate, lobes 10–23 mm, tube gradually expanding into lobes, 7–16 mm; stamens 10, included, ± unequal, 14–26 mm; (ovary stipitate-glandular-hairy). Capsules borne on erect pedicels, 8–20 × 4–6.5 mm, stipitate-glandular-hairy. Seeds without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, loose. 2n = 26.
Phenology: Flowering summer.
Habitat: Stream banks, mesic woods
Elevation: 0-1900 m
Ala., Conn., Ga., Ky., Maine, Md., Mass., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., Va., W.Va.
Individuals of Rhododendron maximum are beautiful, cold-hardy shrubs and are frequently cultivated as ornamentals. Hybrids with R. catawbiense occur. This species has been attributed in standard floras to eastern Canada but not confirmed there by specimens.