Rhododendron occidentale |
Rhododendron arborescens |
|
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California azalea, western azalea |
smooth azalea, sweet azalea |
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Habit | Shrubs or trees, to 8(–10) m, usually not rhizomatous. | Shrubs or trees, to 6 m, usually not rhizomatous. |
Stems | bark smooth to vertically furrowed, shredding; twigs sparsely to densely multicellular stipitate-glandular-hairy or unicellular-hairy, or glabrous, sometimes only unicellular-hairy. |
bark smooth to vertically furrowed, shredding; twigs glabrous or, very rarely, sparsely, widely scattered, unicellular and multicellular eglandular-hairy. |
Leaves | deciduous; petiole multicellular eglandular- or stipitate-glandular-hairy and unicellular-hairy; blade ovate or obovate to elliptic, (2.5–)3.5–8.2(–10.8) × 1.2–2.9(–3.6) cm, thin, membranous, margins entire, plane, ciliate, eglandular-hairy, sometimes also stipitate-glandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous or sparsely unicellular-hairy, often also stipitate-glandular-hairy (or, rarely, stipitate-glandular- and eglandular-hairy), adaxial surface sparsely scattered, multicellular eglandular- and/or stipitate-glandular-hairy and unicellular-hairy, or glabrous. |
deciduous; petiole glabrous or multicellular eglandular-hairy; blade ovate to obovate, 3–8(–10.5) × 1.3–3.5 cm, thin, chartaceous, margins entire, plane, ciliate, eglandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous, (sometimes glaucous), adaxial surface glabrous, (lustrous). |
Inflorescences | 3–15-flowered; bracts similar to bud scales. |
3–7-flowered; bracts similar to bud scales. |
Pedicels | 9–26 mm, stipitate-glandular- and, sometimes, also eglandular-hairy. |
6–21 mm, glabrous or stipitate-glandular-hairy, sometimes also unicellular-hairy. |
Flowers | opening with leaves or after they have expanded, erect to horizontal, fragrant or mephitic-scented; calyx lobes 1–4(–9) mm, often stipitate-glandular- and/or eglandular-hairy, sometimes also unicellular-hairy, margins usually stipitate-glandular-hairy; corolla white with contrasting yellow blotch on upper lobe, white and pink or salmon, or pink with orange blotch on upper lobe, rarely white with yellow lines at throat, or with tube white to red, funnelform, 30–58 mm, stipitate-glandular-hairy and, rarely, also eglandular-hairy, otherwise sparsely to moderately unicellular-hairy or these hairs absent on outer surface, petals connate, lobes 13–29 mm, tube gradually expanding into lobes, 15–29 mm (equaling or longer than lobes); stamens 5, much exserted, ± unequal, 40–75 mm. |
opening after leaves, erect to horizontal, very fragrant; calyx lobes 0.8–6(–9) mm, surfaces and margins scattered, stipitate-glandular- and/or, sometimes, eglandular-hairy; corolla white or, sometimes, light pink (contrasting with dark pink to red style and filaments), without blotch on upper lobe, funnelform, 30–55 mm, stipitate-glandular-hairy (hairs continuing in lines up lobes), otherwise glabrous or sparsely unicellular-hairy on outer surface, petals connate, lobes 10–24 mm, tube ± gradually expanded into lobes, 20–37 mm (equaling or much longer than lobes); stamens 5, much exserted, ± unequal, 44–82 mm. |
Capsules | borne on erect pedicels, 12–22 × 4–14 mm, multicellular stipitate-glandular-hairy, sometimes also eglandular-hairy, otherwise sparsely unicellular-hairy (unicellular hairs rarely absent). |
borne on erect pedicels, 8–17 × 4.5–8 mm, ± densely multicellular stipitate-glandular-hairy, sometimes also sparsely unicellular-hairy. |
Seeds | without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, ± loose. |
without distinct tails; testa not dorsiventrally flattened, usually ± loose. |
Floral | bud scales sparsely to densely unicellular-hairy abaxially, rarely also sparsely eglandular- or stipitate-glandular-hairy, margins unicellular-ciliate, or with glands and cilia mixed, or glandular. |
bud scales usually glabrous abaxially, margins unicellular-ciliate. |
2n | = 26. |
= 26. |
Rhododendron occidentale |
Rhododendron arborescens |
|
Phenology | Flowering spring–summer. | Flowering late spring–summer. |
Habitat | Moist, wooded slopes and canyon bottoms, along streams, thickets, bogs, serpentine ridges, ocean bluffs | Stream banks, rocky streamsides, heath balds, swampy woods or bogs |
Elevation | 0-2700 m (0-8900 ft) | 90-1500 m (300-4900 ft) |
Distribution |
CA; OR
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AL; GA; KY; MD; NC; PA; SC; TN; VA; WV
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Discussion | The flowers of Rhododendron occidentale show an exceptional range of variation in color. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Rhododendron arborescens is most closely related to R. viscosum, as evidenced by their glabrous floral bud scales and flowers that appear after the leaves have expanded (K. A. Kron 1993). It can be distinguished by its glabrous branchlets, red style and filaments (which contrast with the white corollas), and distinctive seeds that lack loose, expanded testae. These two species occasionally hybridize; hybrids with R. cumberlandense also are known. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 467. | FNA vol. 8, p. 470. |
Parent taxa | Ericaceae > subfam. Ericoideae > Rhododendron | Ericaceae > subfam. Ericoideae > Rhododendron |
Sibling taxa | ||
Synonyms | Azalea occidentalis, Azalea californica, R. occidentale var. paludosum, R. sonomense | Azalea arborescens |
Name authority | (Torrey & A. Gray) A. Gray: in W. H. Brewer et al., Bot. California 1: 458. 1876 , | (Pursh) Torrey: Fl. N. Middle United States, 425. 1824 , |
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