Rhododendron albiflorum |
Rhododendron viscosum |
|
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Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron |
clammy azalea, swamp azalea |
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Habit | Shrubs, to 2.5 m, rhizomatous. | Shrubs or trees, to 7 m, rhizomatous or not. |
Stems | bark ± smooth to furrowed; twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy. |
bark smooth to vertically furrowed, shredding; twigs sparsely to conspicuously multicellular eglandular-hairy (hairs unbranched), otherwise glabrous or 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-hairy and unicellular-hairy; blade ovate to obovate, 2–7(–9) × 1–3(–3.8) cm, ± thin, membranous to chartaceous, margins entire or, sometimes, minutely serrulate, plane, ciliate, eglandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous or densely unicellular-hairy, adaxial surface (lustrous or dull), glabrous or sparsely scattered eglandular-hairy, sometimes also sparsely 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. |
3–14-flowered; bracts similar to bud scales. |
Pedicels | to 9–15 mm, eglandular- and stipitate-glandular-hairy. |
5–27 mm, stipitate-glandular- or, sometimes, 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 after leaves, erect to horizontal, slightly to strongly fragrant (most noticeable at night); calyx lobes 0.5–5 mm, surfaces and margins scattered stipitate-glandular-hairy or, sometimes, eglandular-hairy, often also unicellular-hairy; corolla white, sometimes pink-tinged or pink (not strongly contrasting with white or greenish to pinkish style or filaments), without blotch on upper lobe, funnelform, 20–58 mm, usually scattered, often conspicuously stipitate-glandular-hairy (hairs continuing in lines up lobes), otherwise sparsely to moderately unicellular-hairy on outer surface, petals connate, lobes 7–21 mm, tube usually ± gradually expanded into lobes, 13–37 mm (equaling or much longer than lobes); stamens 5, much exserted, ± unequal, 21–65 mm. |
Capsules | borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy. |
borne on erect pedicels, 7–20 × 3–7 mm, usually densely stipitate-glandular- and/or eglandular-hairy, otherwise densely unicellular-hairy to ± glabrous. |
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 or densely unicellular-hairy abaxially (sometimes with sharply marked, dark brown band along distal margins), margins unicellular-ciliate or, sometimes, glandular-serrulate. |
2n | = 26. |
= 26. |
Rhododendron albiflorum |
Rhododendron viscosum |
|
Phenology | Flowering late spring–summer. | Flowering spring–summer. |
Habitat | Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops | Acid swamps, bogs, seepage slopes, pocosins, streamheads and baygalls, wet pine flatwoods, moist pine or pine/oak forests, hummocks, shrub balds |
Elevation | 800-3500 m [2600-11500 ft] | 0-1500 m [0-4900 ft] |
Distribution |
CO; ID; MT; OR; WA; AB; BC
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AL; AR; CT; DE; FL; GA; LA; MA; MD; ME; MS; NC; NH; NJ; NY; OK; PA; RI; SC; TN; TX; VA; VT
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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 viscosum is the most widespread and variable species of sect. Pentanthera and has been divided into as many as four species: R. coryi, R. oblongifolium, R. serrulatum, and R. viscosum in the narrow sense. In addition, minor varieties and forms have been described. Because correlated or geographically coherent sets of character states cannot be discerned within this species, infraspecific taxa are not recognized here (K. A. Kron 1993). Rhododendron viscosum is most closely related to R. arborescens, and possibly also R. atlanticum. Hybrids with R. cumberlandense and R. arborescens are known. Plants with white corollas and a yellow blotch may be the result of hybridization. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 464. | FNA vol. 8, p. 471. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azaleastrum albiflorum, R. albiflorum var. warrenii | Azalea viscosa, Azalea oblongifolia, Azalea serrulata, R. coryi, R. oblongifolium, R. serrulatum, R. viscosum var. serrulatum |
Name authority | Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 , | (Linnaeus) Torrey: Fl. N. Middle United States, 424. 1824 , |
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