Rhododendron prinophyllum

Shrubs, to 3(-5) m, usually not rhizomatous. Stems: bark smooth to vertically furrowed, shredding; twigs scattered, multicellular eglandular-hairy (hairs unbranched), other-wise densely to sparsely unicellular-hairy. Leaves deciduous; petiole usually multicellular eglandular-hairy and unicellular-hairy; blade ovate to obovate, 3-9 × 1.2-3.7 cm, thin, membranous, margins entire, plane, conspicuously ciliate, eglandular-hairy (hairs ascending away from margins), apex acute to obtuse, often mucronate, abaxial surface sparsely to densely unicellular-hairy, sometimes also eglandular-hairy, adaxial surface usually sparsely unicellular-hairy, sometimes glabrous, often also scattered eglandular-hairy. Floral bud scales very sparsely to densely unicellular-hairy abaxially, especially near midvein, margins unicellular-ciliate. Inflorescences 4-13-flowered; bracts similar to bud scales. Pedicels 5-26 mm, usually stipitate-glandular-hairy, or, sometimes, also eglandular-hairy, otherwise sparsely to moderately unicellular-hairy. Flowers opening before or with leaves, erect to horizontal, fragrant (spicy-scented); calyx lobes 0.5-4 mm, surfaces and margins scattered stipitate-glandular- and/or eglandular-hairy, otherwise sparsely to densely unicellular-hairy; corolla usually bright pink, without blotch on upper lobe, funnelform, 25-45 mm, scattered, multicellular stipitate-glandular-hairy (hairs not form-ing distinct lines), otherwise sparsely to moderately unicellular-hairy on outer surface, petals connate, lobes 10-23 mm, tube gradually expanded into lobes, 11-27 mm (equaling or longer than lobes); stamens 5, much exserted, ± unequal, 32-53 mm. Capsules borne on erect pedicel, 10-28 × 3-7 mm, stipitate-glandular-hairy, otherwise sparsely unicellular-hairy. Seeds without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, ± loose. 2n = 26.

Flowering spring. Acidic thickets or bogs, swampy to dry, rocky woods, bluffs, ravines, or along streams; 100-1500 m; Ala., Ark., Conn., Ill., Ky., Md., Mass., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., Tenn., Tex., Vt., Va., W.Va.

Rhododendron prinophyllum is unusual in its strongly disjunct distribution. Plants in the western portion of the range often have longer corolla tubes and are most similar to R. canescens and R. periclymenoides, and can be distinguished from both by their broader, more gradually expanded corolla tubes and usually consistently glandular sepal margins, pedicels, and ovaries. Hybrids are known with R. calendulaceum and R. periclymenoides. The name R. roseum (Loiseleur) Rehder, which has been used for this species, is illegitimate because it was superfluous when published (K. A. Kron 1989).

Much like no. 4 [Rhododendron periclymenoides (Michx.) Shinners], sometimes to 5 m, usually not colonial; winter bud scales pubescent; lvs softly and permanently hairy beneath, with or without setae on the midvein; fls very fragrant; pedicels, cor-tube, and ovary stipitate-glandular; cor bright pink to sometimes nearly white, flat-faced, 4-5 cm wide, the tube about as long as the lobes; stamens ca twice as long as the cor-tube; fr sparsely stipitate-glandular. Moist or dry woods, especially in the mts.; Me. and s. Que. to Va. and Ky.; s. Ill., s. Mo., Ark., and e. Okla. May. (R. roseum; R. canescens, misapplied; Azalea p.; A. rosea, an illegitimate name)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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