Rhododendron tomentosum |
Rhododendron groenlandicum |
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Labrador tea, marsh Labrador tea, northern Labrador tea, trappers tea |
bog Labrador-tea, common Labrador tea, Labrador-tea, rusty Labrador-tea |
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Habit | Shrubs, to 0.5 m, rhizomatous. | Shrubs, 0.2–1.5 m, rhizomatous. |
Stems | creeping or prostrate; bark ± smooth; twigs unicellular-hairy and with flattened, glandular scales, scales often obscured by dense, ferruginous, long-crisped, multicellular hairs. |
erect and/or prostrate; bark smooth, sometimes peeling or shredding with age; twigs unicellular-hairy and with flattened, glandular scales, scales often obscured by dense, ferruginous, long-crisped, unbranched, multicellular hairs. |
Leaves | 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. |
persistent, (fragrant when crushed); petiole with unicellular and/or peltate scales and sometimes ferruginous, long-crisped, multicellular hairs; blade ovate-lanceolate, sometimes narrowly elliptic to linear, 2–5 × 1.5–2.5 cm, coriaceous, margins entire, weakly to strongly revolute, glabrous, apex acute, abaxial surface with sparse to dense glandular-peltate scales without broad rim, scales often obscured by dense (to sparse), ± even covering of ferruginous, long-crisped, unbranched, multicellular, eglandular hairs usually concealing midvein, adaxial surface ± rugose with scattered, lepidote scales and sometimes also unicellular-hairy along sometimes impressed midrib. |
Inflorescences | slightly rounded, 10–35-flowered; bracts lepidote abaxially, margins ciliate, long-crisped-hairy, sometimes also unicellular-hairy. |
slightly rounded, 10–35-flowered; bracts densely lepidote, sometimes with long-crisped hairs abaxially, margins ciliate, hairs long-crisped. |
Pedicels | 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. |
12–25 mm, with unicellular and/or glandular-peltate scales, sometimes multicellular-hairy (hairs ferruginous, long-crisped). |
Flowers | 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. |
radially symmetric, opening after leaves (of flowering shoots), ± erect, not fragrant; calyx lobes ca. 1–1.5 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 densely unicellular-hairy, petals appearing distinct or only slightly connate basally, lobes 5–7 mm; stamens (5–)8(–10), exserted, ± equal, 3.8–9.5(–11) mm; filaments glabrous or proximally unicellular-hairy. |
Capsules | 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. |
borne on broadly recurved pedicels, 3–5.5 × 4–6 mm (slightly longer than wide), with sparse, lepidote scales, sometimes also long-crisped-hairy, acropetally dehiscent. |
Seeds | somewhat elongated beyond narrow ends; testa closely appressed. |
somewhat elongated beyond narrow ends; testa closely appressed. |
Floral | bud scales with lepidote scales and unicellular-hairy abaxially, margins unicellular-hairy. |
bud scales with lepidote scales, unicellular-hairy abaxially, margins unicellular-hairy. |
2n | = 26, 52. |
= 26. |
Rhododendron tomentosum |
Rhododendron groenlandicum |
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Phenology | Flowering spring–summer. | Flowering spring-mid summer. |
Habitat | Bogs, muskeg, tundra, raised beach ridges | Bogs, spruce forests, muskeg, swamps, stream margins, talus slopes, tundra |
Elevation | 0-1800 m (0-5900 ft) | 0-2000 m (0-6600 ft) |
Distribution |
AK; AB; BC; MB; NF; NT; NU; ON; QC; SK; YT; Greenland; Europe; Asia
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AK; CT; ID; MA; ME; MI; MN; NH; NY; OR; PA; VT; WA; WI; AB; BC; MB; NB; NF; NS; NT; NU; ON; PE; QC; SK; YT; Greenland
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Discussion | Rhododendron groenlandicum, R. columbianum, and R. tomentosum customarily have been placed in the genus Ledum. Ledum is here considered to be a subsection of Rhododendron subg. Rhododendron (as subsect. Ledum), a placement supported by the presence in these species of comparable complex, multicellular, glandular, peltate scales and phylogenetic analyses of morphological and molecular data. The glandular scales of species of subsect. Ledum lack the radiating, broad-rimmed fringe-cells found in some members of subg. Rhododendron (and characteristic of R. minus and R. lapponicum) but are essentially identical to those of species of subsect. Edgeworthia, e.g., R. pendulum (see K. A. Kron and W. S. Judd 1990). More than 500 species of subg. Rhododendron occur in tropical and temperate eastern Asia (J. Cullen 1980; D. F. Chamberlain et al. 1996). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Source | FNA vol. 8, p. 459. | FNA vol. 8, p. 460. |
Parent taxa | Ericaceae > subfam. Ericoideae > Rhododendron | Ericaceae > subfam. Ericoideae > Rhododendron |
Sibling taxa | ||
Synonyms | Ledum palustre, Ledum decumbens, Ledum palustre subsp. decumbens, R. subarcticum, R. tolmachevii, R. tomentosum subsp. decumbens, R. tomentosum var. subarcticum | Ledum groenlandicum |
Name authority | Harmaja: Ann. Bot. Fenn. 27: 204. (1990) | (Oeder) Kron & Judd: Syst. Bot. 15: 67. 1990 , |
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