Rhododendron calendulaceum |
Rhododendron tomentosum |
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flame azalea |
Labrador tea, marsh Labrador tea, northern Labrador tea, trappers tea |
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Habit | Shrubs or trees, to 4(–10) m, usually not rhizomatous. | Shrubs, to 0.5 m, rhizomatous. |
Stems | bark smooth to vertically furrowed, shredding; twigs sparsely to conspicuously multicellular eglandular-hairy (hairs unbranched), otherwise sparsely to moderately 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-hairy and unicellular-hairy; blade ovate to obovate, 4.5–9.1 × 1.3–3.3 cm, thin, membranous to chartaceous, margins entire, plane, ciliate, eglandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous or densely eglandular-hairy, often also very sparsely to moderately unicellular-hairy, adaxial surface glabrous or sparsely scattered eglandular-hairy, often also sparsely unicellular-hairy. |
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 | 5–9-flowered; bracts similar to bud scales. |
slightly rounded, 10–35-flowered; bracts lepidote abaxially, margins ciliate, long-crisped-hairy, sometimes also unicellular-hairy. |
Pedicels | 7–14 mm, stipitate-glandular-hairy and/or eglandular-hairy, otherwise sparsely to densely unicellular-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 | opening before or as leaves expand, erect to horizontal, acrid-scented; calyx lobes 1–3 mm, scattered usually stipitate-glandular-hairy and unicellular-hairy, margins long stipitate-glandular-hairy and/or eglandular-hairy; corolla orange to red-orange, with contrasting, darker-colored, orange to yellow blotch on upper lobe, funnelform, 30–54 mm, densely multicellular stipitate-glandular-hairy, otherwise sparsely to densely unicellular-hairy on outer surface, petals connate, lobes 14–30 mm, (spreading nearly as broadly as tube is long), tube abruptly expanding into lobes, 16–28 mm (longer than lobes); stamens 5, much exserted, ± unequal, 52–72 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, 15–29 × 5–9 mm, sparsely to moderately long stipitate-glandular-hairy and/or eglandular-hairy, and sparsely 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 | without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, ± loose. |
somewhat elongated beyond narrow ends; testa closely appressed. |
Floral | bud scales usually glabrous abaxially, margins glandular. |
bud scales with lepidote scales and unicellular-hairy abaxially, margins unicellular-hairy. |
2n | = 52. |
= 26, 52. |
Rhododendron calendulaceum |
Rhododendron tomentosum |
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Phenology | Flowering spring–summer. | Flowering spring–summer. |
Habitat | Mixed deciduous forests | Bogs, muskeg, tundra, raised beach ridges |
Elevation | 200-1000 m (700-3300 ft) | 0-1800 m (0-5900 ft) |
Distribution |
GA; KY; MD; NC; OH; PA; SC; TN; VA; WV
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AK; AB; BC; MB; NF; NT; NU; ON; QC; SK; YT; Greenland; Europe; Asia
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Discussion | Rhododendron calendulaceum, frequently confused with the diploid R. cumberlandense, is an allotetraploid, and may have been derived from a hybrid between an ancestor of R. cumberlandense and one of R. prinophyllum (K. A. Kron 1993). It is distinguished from R. cumberlandense by its flowers opening before or with (versus after) the expansion of the leaves, glandular or eglandular (versus usually eglandular) pedicels, glandular or eglandular (versus usually eglandular) sepal margins (R. cumberlandense never with both pedicels and sepal margins glandular), and nonglaucous (versus often glaucous) abaxial leaf surface. Rhododendron calendulaceum is one of the showiest shrubs of the southern Appalachians; it is known to hybridize with R. prinophyllum and R. canescens. Rhododendron calendulaceum and the remaining species (through 25. R. eastmanii) are the North American representatives of sect. Pentanthera G. Don, a group characterized by corollas that are typically unicellular-hairy on the outside and with a narrow tube, flowers with five, declinate, and usually much-exserted stamens, and seeds with ± loose testae (K. A. Kron 1993; Kron and M. Creel 1999). All species are used as ornamentals because of their colorful flowers(F. C. Galle 1985). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Source | FNA vol. 8, p. 465. | FNA vol. 8, p. 459. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Azalea calendulacea | Ledum palustre, Ledum decumbens, Ledum palustre subsp. decumbens, R. subarcticum, R. tolmachevii, R. tomentosum subsp. decumbens, R. tomentosum var. subarcticum |
Name authority | (Michaux) Torrey: Fl. N. Middle United States, 425. 1824 , | Harmaja: Ann. Bot. Fenn. 27: 204. (1990) |
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