Rhododendron minus |
Rhododendron calendulaceum |
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Piedmont rhododendron |
flame azalea |
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Habit | Shrubs, to 3(–5) mm, often rhizomatous. | Shrubs or trees, to 4(–10) m, usually not rhizomatous. | ||||
Stems | bark smooth to vertically furrowed, shredding; twigs with ferrugineous, multicellular, broad-rimmed, glandular-peltate scales. |
bark smooth to vertically furrowed, shredding; twigs sparsely to conspicuously multicellular eglandular-hairy (hairs unbranched), otherwise sparsely to moderately unicellular-hairy. |
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Leaves | persistent; petiole with ferruginous, broad-rimmed, glandular-peltate scales and unicellular-hairy; blade narrowly elliptic to elliptic or oval, sometimes obovate, (1–)5–8(–13) × (1–)2–3.5(–5.5) cm, thick, coriaceous, margins entire, plane to conspicuously revolute, with scattered, glandular-peltate scales, apex acute or acuminate or obtuse to rounded, surfaces with scattered, ferruginous, broad-rimmed, glandular-peltate scales abaxially, (scales ± deciduous adaxially). |
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. |
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Inflorescences | 5–10-flowered; bracts similar to bud scales. |
5–9-flowered; bracts similar to bud scales. |
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Pedicels | 5–15 mm, with ferruginous scales. |
7–14 mm, stipitate-glandular-hairy and/or eglandular-hairy, otherwise sparsely to densely unicellular-hairy. |
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Flowers | opening before or after development of leaves, erect to horizontal, fragrant; calyx lobes 0.5–2 mm, with ferruginous scales; corolla dark to very pale pink or white, upper lobe usually with greenish spots, campanulate to funnelform, 15–37 mm, with scattered, ferruginous, peltate scales on outer surface, petals connate (for 3/4+ their lengths), lobes 8–19 mm, tube gradually expanding into lobes, 8–22 mm; stamens 10, included to slightly exserted, ± unequal, 13–26 mm. |
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. |
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Capsules | borne on erect pedicels, 6–14 × 2.9–5 mm, with ferruginous, peltate scales. |
borne on erect pedicels, 15–29 × 5–9 mm, sparsely to moderately long stipitate-glandular-hairy and/or eglandular-hairy, and sparsely unicellular-hairy. |
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Seeds | with short, blunt/truncate tails at each end; testa closely appressed. |
without distinct tails, flattened portion of testa well developed at each end; testa expanded, dorsiventrally flattened, ± loose. |
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Floral | bud scales ferruginous-lepidote, sometimes also unicellular-hairy abaxially, margins unicellular-ciliate. |
bud scales usually glabrous abaxially, margins glandular. |
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2n | = 26. |
= 52. |
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Rhododendron minus |
Rhododendron calendulaceum |
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Phenology | Flowering spring–summer. | |||||
Habitat | Mixed deciduous forests | |||||
Elevation | 200-1000 m (700-3300 ft) | |||||
Distribution |
AL; FL; GA; NC; SC; TN
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GA; KY; MD; NC; OH; PA; SC; TN; VA; WV
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Discussion | Varieties 2 (2 in the flora). Rhododendron minus is here circumscribed broadly, including R. carolinianum and R. chapmanii, and the latter is considered to be a distinct variety (W. H. Duncan and T. M. Pullen 1962). Variety chapmanii is federally listed. This species is often grown as an ornamental. Rhododendron minus and R. lapponicum are members of subg. Rhododendron, as indicated by their glandular-peltate scales; the subgenus is represented by hundreds of species in eastern and southern Asia (see J. Cullen 1980). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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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Key |
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Source | FNA vol. 8, p. 460. | FNA vol. 8, p. 465. | ||||
Parent taxa | Ericaceae > subfam. Ericoideae > Rhododendron | Ericaceae > subfam. Ericoideae > Rhododendron | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | Azalea calendulacea | |||||
Name authority | Michaux: J. Hist. Nat. 1: 412. 1792 , | (Michaux) Torrey: Fl. N. Middle United States, 425. 1824 , | ||||
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