Rhododendron macrophyllum |
Rhododendron prinophyllum |
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big leaf rhododendron, California rhododendron, California rose bay, coast rhododendron, Pacific rhododendron, western rhododendron |
early azalea, election-pink, hoary azalea, roseshell azalea |
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Habit | Shrubs or trees, to 5 m, sometimes rhizomatous. | Shrubs, to 3(–5) m, usually not rhizomatous. |
Stems | bark smooth to vertically furrowed, shredding; twigs with basally branched, crisped/matted, eglandular hairs, very quickly glabrate. |
bark smooth to vertically furrowed, shredding; twigs scattered, multicellular eglandular-hairy (hairs unbranched), otherwise densely to sparsely unicellular-hairy. |
Leaves | persistent; petiole glabrous; blade elliptic to slightly ovate or obovate, (6–)8.5–14(–20) × 2.5–5.5(–7.5) cm, thick, coriaceous, margins entire, plane to revolute, glabrous, apex acute to obtuse or slightly acuminate, surfaces scattered eglandular-hairy (hairs branched basally, crisped, very quickly deciduous), abaxial surface ± smooth. |
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. |
Inflorescences | 10–20-flowered; bracts similar to bud scales. |
4–13-flowered; bracts similar to bud scales. |
Pedicels | 30–60 mm, glabrous. |
5–26 mm, usually stipitate-glandular-hairy, or, sometimes, also eglandular-hairy, otherwise sparsely to moderately unicellular-hairy. |
Flowers | opening after development of leaves (of flowering shoots), erect to horizontal, fragrant; calyx lobes 1–1.5 mm, glabrous, except margins eglandular- and stipitate-glandular-hairy; corolla white to pink or rose-purple, with yellowish green spots on upper lobe, broadly campanulate, 24–48 mm, outer surface glabrous, petals connate, lobes 14–30 mm, tube gradually expanding into lobes, 10–23 mm; stamens 10, included, ± unequal, 16–37 mm. |
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 forming 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 pedicels, 13–25 × 4–7 mm, eglandular-hairy (hairs ferruginous, branched or unbranched) and, often, stipitate-glandular-hairy. |
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. |
without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, ± loose. |
Floral | bud scales multicellular eglandular-hairy (hairs branched basally), and unicellular-hairy (hairs short to elongate) abaxially, margins eglandular-hairy (hairs branched). |
bud scales very sparsely to densely unicellular-hairy abaxially, especially near midvein, margins unicellular-ciliate. |
2n | = 26. |
= 26. |
Rhododendron macrophyllum |
Rhododendron prinophyllum |
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Phenology | Flowering spring–summer. | Flowering spring. |
Habitat | Forest and forest margins, thickets | Acidic thickets or bogs, swampy to dry, rocky woods, bluffs, ravines, or along streams |
Elevation | 50-1600 m [160-5200 ft] | 100-1500 m [300-4900 ft] |
Distribution |
CA; OR; WA; BC
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AL; AR; CT; IL; KY; MA; MD; MO; NC; NH; NJ; NY; OH; OK; PA; RI; TN; TX; VA; VT; WV
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Discussion | Rhododendron macrophyllum, R. maximum, and R. catawbiense represent subg. Hymenanthes (Blume) K. Koch in North America; the subgenus is represented by hundreds of species in temperate eastern Asia and is characterized by its branched, eglandular hairs (D. F. Chamberlain 1982). These showy plants are frequently used as ornamentals. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 462. | FNA vol. 8, p. 469. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | R. californicum | Azalea prinophylla |
Name authority | D. Don ex G. Don: Gen. Hist. 3: 843. 1834 , | (Small) Millais: Rhododendrons, 229. 1917 , |
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