Rhododendron albiflorum |
Rhododendron tomentosum |
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Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron |
Labrador tea, marsh Labrador tea, northern Labrador tea, trappers tea |
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Habit | Shrubs, to 2.5 m, rhizomatous. | Shrubs, to 0.5 m, rhizomatous. |
Stems | bark ± smooth to furrowed; twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy. |
creeping or prostrate; bark ± smooth; twigs unicellular-hairy and with flattened, glandular scales, scales often obscured by dense, ferruginous, long-crisped, multicellular hairs. |
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, (fragrant when crushed); petiole with unicellular and/or peltate scales and, sometimes, ferruginous, long-crisped hairs; blade ± linear, 2–5 × 1–4 cm (often much longer than wide), coriaceous, margins entire, revolute, glabrous, apex acute, abaxial surface with sparse to dense, glandular-peltate scales without broad rim, scales often obscured by dense (to sparse), ferruginous, long-crisped, multicellular hairs sometimes forming dense, ± uniform mat, adaxial surface rugose with scattered, lepidote scales and sometimes also with white, unicellular hairs along impressed midrib, midrib usually lanate. |
Inflorescences | lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered; bracts similar to bud scales. |
slightly rounded, 10–35-flowered; bracts lepidote abaxially, margins ciliate, long-crisped-hairy, sometimes also unicellular-hairy. |
Pedicels | to 9–15 mm, eglandular- and stipitate-glandular-hairy. |
5–26 mm, sparsely eglandular-hairy (hairs ferruginous, elongated), with ferruginous, long-crisped, unicellular and/or peltate scales, sometimes also long-stalked, 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. |
radially symmetric, opening after leaves (of flowering shoots), ± erect, not fragrant; calyx lobes ca. 1 mm, outer surface densely to sparsely unicellular-hairy (hairs tan), and multicellular, stipitate-glandular-hairy (hairs red) on margins; corolla white to cream, without blotch, ± rotate, 2–8 mm, inner surface often densely unicellular-hairy, petals appearing distinct or only slightly connate basally, lobes 5–7 mm; stamens 10, exserted, ± equal, 4.4–8.5 mm. |
Capsules | borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy. |
borne on apex of sharply recurved pedicels, 2.5–5 × 1–3 mm (only slightly longer than wide), with sparse to dense, lepidote scales, acropetally dehiscent. |
Seeds | with distinct tails; testa closely appressed. |
somewhat elongated beyond narrow ends; testa closely appressed. |
Floral | bud scales stipitate-glandular- and eglandular-hairy abaxially, margins stipitate-glandular-hairy. |
bud scales with lepidote scales and unicellular-hairy abaxially, margins unicellular-hairy. |
2n | = 26. |
= 26, 52. |
Rhododendron albiflorum |
Rhododendron tomentosum |
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Phenology | Flowering late spring–summer. | Flowering spring–summer. |
Habitat | Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops | Bogs, muskeg, tundra, raised beach ridges |
Elevation | 800-3500 m [2600-11500 ft] | 0-1800 m [0-5900 ft] |
Distribution |
CO; ID; MT; OR; WA; AB; BC
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AK; AB; BC; MB; NF; NT; NU; ON; QC; SK; YT; Greenland; Europe; Asia
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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.) |
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Source | FNA vol. 8, p. 464. | FNA vol. 8, p. 459. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azaleastrum albiflorum, R. albiflorum var. warrenii | Ledum palustre, Ledum decumbens, Ledum palustre subsp. decumbens, R. subarcticum, R. tolmachevii, R. tomentosum subsp. decumbens, R. tomentosum var. subarcticum |
Name authority | Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 , | Harmaja: Ann. Bot. Fenn. 27: 204. (1990) |
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