Rhododendron albiflorum |
Rhododendron austrinum |
|
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Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron |
Florida azalea, orange azalea |
|
Habit | Shrubs, to 2.5 m, rhizomatous. | Shrubs or trees, to 3(–5) m, usually not rhizomatous. |
Stems | bark ± smooth to furrowed; twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy. |
bark smooth to vertically furrowed, shredding; twigs conspicuously multicellular stipitate-glandular-hairy, otherwise ± moderately to densely unicellular-hairy. |
Leaves | deciduous; petiole multicellular eglandular- and stipitate-glandular-hairy and unicellular-hairy; blade narrowly elliptic or ovate to obovate, 2–9 × 0.8–3 cm, thin, membranous to chartaceous, margins minutely serrate, plane, ciliate when young, eglandular- and stipitate-glandular-hairy, apex acute to ± rounded, surfaces scattered eglandular-hairy, ± glabrescent. |
deciduous; petiole multicellular stipitate-glandular-hairy and unicellular-hairy; blade ovate to obovate, 3–11 × 1.5–4.5 cm, thin, membranous, margins entire, plane, ciliate, eglandular- and stipitate-glandular-hairy, apex acute to obtuse, often mucronate, abaxial surface ± moderately unicellular-hairy, adaxial surface sparsely scattered stipitate-glandular-hairy, otherwise ± moderately unicellular-hairy, rarely glabrescent. |
Inflorescences | lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered; bracts similar to bud scales. |
9–24-flowered; bracts similar to bud scales. |
Pedicels | to 9–15 mm, eglandular- and stipitate-glandular-hairy. |
5–17 mm, stipitate-glandular-hairy, otherwise ± densely unicellular-hairy. |
Flowers | ± radially symmetric, opening soon after (and borne below) expanded leaves, pendulous, very fragrant (similar to vanilla and jasmine); calyx lobes 5–17 mm, eglandular- and stipitate-glandular-hairy, margins glandular-hairy; corolla white, rarely marked with yellow, bowl-shaped, 9–22 mm, minutely unicellular-hairy or glabrous on outer surface, petals connate, lobes 6–15 mm, tube expanding into lobes, 3–9 mm; stamens 9(–12), included, ± unequal, 5.5–14 mm. |
opening before or with leaves, erect to horizontal, slightly or not fragrant; calyx lobes 0.5–2.5 mm, scattered stipitate-glandular-hairy, otherwise unicellular-hairy, margins long stipitate-glandular-hairy; corolla yellow to orange, with usually red or orange-red tube, with indistinct, darker yellow, orange, or red blotch on upper lobe, funnelform, 25–45 mm, scattered stipitate-glandular-hairy, otherwise ± moderately unicellular-hairy on outer surface, petals connate, lobes 9–20 mm, tube ± gradually expanded into lobes, 15–25 mm (longer than lobes); stamens 5, much exserted, ± unequal, 52–77 mm. |
Capsules | borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy. |
borne on erect pedicels, 14–26 × 3–5.5 mm, sparsely to densely stipitate-glandular-hairy, otherwise moderately to densely unicellular-hairy. |
Seeds | with distinct tails; testa closely appressed. |
without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, ± loose. |
Floral | bud scales stipitate-glandular- and eglandular-hairy abaxially, margins stipitate-glandular-hairy. |
bud scales densely to moderately unicellular-hairy abaxially, margins unicellular-ciliate, also partly glandular-serrate. |
2n | = 26. |
= 26. |
Rhododendron albiflorum |
Rhododendron austrinum |
|
Phenology | Flowering late spring–summer. | Flowering spring. |
Habitat | Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops | Wooded slopes, bluffs or lowlands along streams |
Elevation | 800-3500 m [2600-11500 ft] | 0-100 m [0-300 ft] |
Distribution |
CO; ID; MT; OR; WA; AB; BC
|
AL; FL; GA; MS
|
Discussion | Rhododendron albiflorum is especially distinctive due to its axillary, white, somewhat pendulous, and nearly actinomorphic flowers, and it is placed in the monotypic subg. Candidastrum (Sleumer) Philipson & Philipson (W. R. Philipson and M. N. Philipson 1986). It is occasionally used as an ornamental. The disjunct population in Colorado has somewhat smaller calyx lobes and corollas and shorter stamens; it is sometimes recognized as var. warrenii (M. A. Lane et al. 1993). This variety is not recognized here because of the extent of morphological overlap between that population and those of the Pacific Northwest. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Rhododendron austrinum is most closely related to R. luteum Sweet of eastern Europe, Turkey, and the Caucasus region and to R. occidentale (K. A. Kron 1993). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 464. | FNA vol. 8, p. 466. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azaleastrum albiflorum, R. albiflorum var. warrenii | Azalea austrina |
Name authority | Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 , | (Small) Rehder: in L. H. Bailey, Stand. Cycl. Hort. 6: 3571. 1917 , |
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