Rhododendron albiflorum |
Rhododendron canescens |
|
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Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron |
mountain azalea, Piedmont or southern pinxterbloom azalea |
|
Habit | Shrubs, to 2.5 m, rhizomatous. | Shrubs or trees, to 6 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 scattered, multicellular eglandular- and/or stipitate-glandular-hairy (hairs unbranched), 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 usually multicellular eglandular- or stipitate-glandular-hairy, also unicellular-hairy; blade ovate to obovate, 2.5–10(–13) × 1.2–3(–4) cm, thin, membranous to chartaceous, margins entire, rarely minutely serrulate, plane, inconspicuously ciliate, eglandular-hairy (hairs appressed to margins), apex acute to obtuse, often mucronate, abaxial surface densely to sparsely unicellular-hairy, sometimes glabrous or glabrate, often also scattered eglandular-hairy, adaxial surface usually scattered eglandular-hairy, otherwise sparsely unicellular-hairy, sometimes glabrous. |
Inflorescences | lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered; bracts similar to bud scales. |
6–19-flowered; bracts similar to bud scales. |
Pedicels | to 9–15 mm, eglandular- and stipitate-glandular-hairy. |
4–17 mm, usually eglandular-hairy, rarely stipitate-glandular- and/or eglandular-hairy, otherwise sparsely to 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, fragrant (usually musky-scented); calyx lobes 0.5–4 mm, surfaces and margins scattered stipitate-glandular- and/or eglandular-hairy, otherwise usually densely unicellular-hairy; corolla deep pink to white with pink tube, without blotch on upper lobe, funnelform, 23–46 mm, scattered, multicellular stipitate-glandular-hairy (hairs not forming distinct lines), otherwise sparsely to densely unicellular-hairy on outer surface, petals connate, lobes 7–20 mm, tube ± gradually expanded into lobes, 13–27 mm (equaling or longer than lobes); stamens 5, much exserted, ± unequal, 31–64 mm. |
Capsules | borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy. |
borne on erect pedicels, 12–33 × 3–6.5 mm, usually sparsely to moderately eglandular-hairy, otherwise ± 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 unicellular-hairy abaxially, margins usually unicellular-ciliate. |
2n | = 26. |
= 26. |
Rhododendron albiflorum |
Rhododendron canescens |
|
Phenology | Flowering late spring–summer. | Flowering spring. |
Habitat | Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops | Moist to dry woods, pocosins, swamps and savannas, often along streams |
Elevation | 800-3500 m [2600-11500 ft] | 0-500 m [0-1600 ft] |
Distribution |
CO; ID; MT; OR; WA; AB; BC
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AL; AR; FL; GA; IL; KY; LA; MS; NC; OK; SC; TN; TX
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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 canescens is most similar to R. prinophyllum and R. periclymenoides, although these three species do not constitute a clade (K. A. Kron 1993); they occasionally hybridize where their habitats and ranges overlap. In addition, putative hybrids with R. alabamense, R. atlanticum, R. austrinum, R. flammeum, R. periclymenoides, and R. calendulaceum are known. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 464. | FNA vol. 8, p. 469. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azaleastrum albiflorum, R. albiflorum var. warrenii | Azalea canescens, Azalea candida |
Name authority | Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 , | (Michaux) Sweet: Hort. Brit. ed. 2, 343. 1830 , |
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