Rhododendron albiflorum |
Rhododendron maximum |
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Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron |
great laurel, great rosebay, rhododendron, rosebay, rosebay rhododendron |
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Habit | Shrubs, to 2.5 m, rhizomatous. | Shrubs or trees, to 10 m, sometimes rhizomatous. |
Stems | bark ± smooth to furrowed; twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy. |
bark smooth to vertically furrowed, shredding; twigs multicellular stipitate-glandular-hairy and eglandular-hairy (hairs basally branched, crisped/matted), glabrate in age. |
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. |
persistent; petiole multicellular-hairy (hairs ± branched), often glabrescent; blade oblong to obovate or elliptic, (6–)9–20(–31) × (1.5–)2–5(–8) cm (length/width ratio 2.4–8), thick, coriaceous, margins entire, revolute to ± plane, glabrous or sparsely hairy (hairs branched), apex acuminate to sometimes acute, surfaces scattered stipitate-glandular-hairy and eglandular-hairy (hairs forming dense mat, basally branched, crisped, abaxially becoming sticky and matted, forming ± scaly or continuous, pale, shellaclike coating, smooth to slightly roughened, hairs ± deciduous adaxially). |
Inflorescences | lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered; bracts similar to bud scales. |
10–25-flowered; bracts similar to bud scales. |
Pedicels | to 9–15 mm, eglandular- and stipitate-glandular-hairy. |
17–60 mm, multicellular stipitate-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 development of leaves (of flowering shoots), erect to horizontal, not or only slightly fragrant; calyx lobes 2–6 mm, stipitate-glandular-hairy; corolla white to pink, rarely deep pink to purple, with yellowish green spots on upper lobe, campanulate, 20–36 mm, scattered stipitate-glandular-hairy on outer surface, petals connate, lobes 10–23 mm, tube gradually expanding into lobes, 7–16 mm; stamens 10, included, ± unequal, 14–26 mm; (ovary stipitate-glandular-hairy). |
Capsules | borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy. |
borne on erect pedicels, 8–20 × 4–6.5 mm, stipitate-glandular-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 stipitate-glandular-hairy, eglandular-hairy (hairs ferruginous, crisped), and short unicellular-hairy abaxially, margins hairy (hairs branched, long-celled). |
2n | = 26. |
= 26. |
Rhododendron albiflorum |
Rhododendron maximum |
|
Phenology | Flowering late spring–summer. | Flowering summer. |
Habitat | Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops | Stream banks, mesic woods |
Elevation | 800-3500 m [2600-11500 ft] | 0-1900 m [0-6200 ft] |
Distribution |
CO; ID; MT; OR; WA; AB; BC
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AL; CT; GA; KY; MA; MD; ME; NC; NH; NJ; NY; OH; PA; RI; SC; TN; VA; VT; WV
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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.) |
Individuals of Rhododendron maximum are beautiful, cold-hardy shrubs and are frequently cultivated as ornamentals. Hybrids with R. catawbiense occur. This species has been attributed in standard floras to eastern Canada but not confirmed there by specimens. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 8, p. 464. | FNA vol. 8, p. 463. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azaleastrum albiflorum, R. albiflorum var. warrenii | R. ashleyi |
Name authority | Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 , | Linnaeus: Sp. Pl. 1: 392. 1753 , |
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