Rhododendron albiflorum |
Rhododendron eastmanii |
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Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron |
May white azalea, santee azalea |
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Habit | Shrubs, to 2.5 m, rhizomatous. | Shrubs or trees, to 5 m, not rhizomatous. |
Stems | bark ± smooth to furrowed; twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy. |
bark smooth to vertically furrowed, shredding; twigs unicellular and multicellular eglandular-hairy and 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 densely unicellular-hairy and sparsely to densely multicellular eglandular-hairy; blade ovate or obovate to elliptic, 4.3–7.1 × 1.8–2.9 cm, membranous, margins entire, plane, ciliate, multicellular eglandular-hairy, apex acute to obtuse, mucronate, surfaces sparsely scattered, multicellular eglandular-hairy, abaxial surface moderately to densely unicellular-hairy and multicellular eglandular-hairy, midvein densely unicellular-hairy and multicellular eglandular-hairy, secondary veins sometimes multicellular eglandular-hairy, adaxial surface sparsely to densely unicellular-hairy, midvein densely unicellular-hairy. |
Inflorescences | lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered; bracts similar to bud scales. |
5–9 flowered; bracts similar to bud scales. |
Pedicels | to 9–15 mm, eglandular- and stipitate-glandular-hairy. |
5–11 mm, densely unicellular-hairy and sparsely to densely multicellular eglandular-hairy, sometimes multicellular glandular-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 after leaves have expanded, erect to horizontal, strongly fragrant (fresh during mid day); calyx lobes 0.5–1 mm (often varying in length on same flower), margins setose, multicellular eglandular-hairy, abaxial surface sparsely to densely unicellular-hairy and multicellular eglandular-hairy, sometimes sparsely multicellular, weakly glandular-hairy; corolla white, lobes pink tinged on newly opened flowers, with yellow to orange blotch on upper lobe (style white), funnelform, 24–50 mm, outer surface densely unicellular-hairy and sparsely to densely multicellular stipitate-glandular-hairy (glands usually weakly developed), inner surface densely unicellular-hairy, petals connate, upper lobe 9–17 mm, lateral lobes 11–25 mm, tube gradually expanding into lobes, 13–25 mm (equaling or much longer than lobes); stamens 5, exserted, ± unequal, 45–67 mm. |
Capsules | borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy. |
borne on erect pedicels, 12–19 × 4–8 mm, sparsely to densely unicellular-hairy and multicellular eglandular-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 glabrous abaxially, margins unicellular-ciliate near apex, glandular along proximal 2/3. |
2n | = 26. |
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Rhododendron albiflorum |
Rhododendron eastmanii |
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Phenology | Flowering late spring–summer. | Flowering late spring–early summer. |
Habitat | Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops | Forests on north-facing slopes near limestone |
Elevation | 800-3500 m [2600-11500 ft] | 30-200 m [100-700 ft] |
Distribution |
CO; ID; MT; OR; WA; AB; BC
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SC |
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.) |
Older collections of Rhododendron eastmanii were typically referred to R. alabamense, which flowers early in the spring before the leaves have expanded, and has inflorescence bud scales are unicellular-ciliate; in R. eastmanii the bud scale margins are glandular. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 464. | FNA vol. 8, p. 473. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azaleastrum albiflorum, R. albiflorum var. warrenii | |
Name authority | Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 , | Kron & Creel: Novon 9: 377, figs. 1, 2. 1999 , |
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