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Lapland rhododendron, Lapland rose-bay

flame azalea

Habit Shrubs, to 0.5(–0.7) m, rhizomatous. Shrubs or trees, to 4(–10) m, usually not rhizomatous.
Stems

prostrate to erect;

bark ± smooth to vertically furrowed, shredding;

twigs with straw-colored to ferruginous, multicellular, broad-rimmed, peltate scales and unicellular-hairy.

bark smooth to vertically furrowed, shredding;

twigs sparsely to conspicuously multicellular eglandular-hairy (hairs unbranched), otherwise sparsely to moderately unicellular-hairy.

Leaves

persistent;

petiole with broad-rimmed, glandular-peltate scales;

blade oblong-elliptic to elliptic, ovate, or obovate, 0.4–2(–2.5) × 0.2–0.7(–0.9) cm, coriaceous, margins entire, plane to revolute, with broad-rimmed scales, apex obtuse to rounded or mucronate, surfaces with conspicuous, straw-colored or golden to ferruginous, broad-rimmed, glandular-peltate scales and unicellular-hairy abaxially.

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.

Inflorescences

fasciculate racemes, 3–6-flowered;

bracts similar to bud scales.

5–9-flowered;

bracts similar to bud scales.

Pedicels

2.5–14 mm, with ferruginous scales and often unicellular-hairy.

7–14 mm, stipitate-glandular-hairy and/or eglandular-hairy, otherwise sparsely to densely unicellular-hairy.

Flowers

opening before development of leaves, erect to horizontal, fragrant;

calyx lobes 0.5–2 mm, with ferruginous scales and unicellular-hairy, margins ciliate, unicellular and multicellular eglandular-hairy;

corolla rose to purple, sometimes white, without blotch, broadly funnelform, (6.5–)7.5–14(–15) mm, glabrous on outer surface, petals connate (for 3/4+ their lengths), lobes 4.5–8.5 mm, tube gradually expanding into lobes, 1.5–6.5 mm;

stamens 5–10, slightly exserted, ± unequal, 7–13 mm;

filaments glabrous or proximally unicellular-hairy.

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.

Capsules

borne on erect pedicels, 4–7 × 2–3 mm, with ferruginous, peltate scales and unicellular-hairy.

borne on erect pedicels, 15–29 × 5–9 mm, sparsely to moderately long stipitate-glandular-hairy and/or eglandular-hairy, and sparsely unicellular-hairy.

Seeds

without 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 ferruginous-lepidote, sometimes also unicellular-hairy abaxially, margins ± ciliate, unicellular and multicellular, elongate eglandular-hairy.

bud scales usually glabrous abaxially, margins glandular.

2n

= 26, 52.

= 52.

Rhododendron lapponicum

Rhododendron calendulaceum

Phenology Flowering spring–summer. Flowering spring–summer.
Habitat Arctic and alpine tundra, rocky barrens and heaths or thickets, raised beach ridges, sandy stream banks Mixed deciduous forests
Elevation 0-1900 m (0-6200 ft) 200-1000 m (700-3300 ft)
Distribution
from FNA
AK; ME; NH; NY; WI; AB; BC; MB; NF; NS; NT; NU; ON; QC; YT; Greenland; Europe (Russia, Scandinavia); Asia (Siberia)
[WildflowerSearch map]
[BONAP county map]
from FNA
GA; KY; MD; NC; OH; PA; SC; TN; VA; WV
[WildflowerSearch map]
[BONAP county map]
Discussion

Rhododendron lapponicum is known to hybridize with R. tomentosum in Greenland, producing R. ×vanhoeffenii Abromeit.

(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.)

Source FNA vol. 8, p. 462. FNA vol. 8, p. 465.
Parent taxa Ericaceae > subfam. Ericoideae > Rhododendron Ericaceae > subfam. Ericoideae > Rhododendron
Sibling taxa
R. alabamense, R. albiflorum, R. arborescens, R. atlanticum, R. austrinum, R. calendulaceum, R. canadense, R. canescens, R. catawbiense, R. columbianum, R. cumberlandense, R. eastmanii, R. flammeum, R. groenlandicum, R. macrophyllum, R. maximum, R. minus, R. occidentale, R. periclymenoides, R. prinophyllum, R. prunifolium, R. tomentosum, R. vaseyi, R. viscosum
R. alabamense, R. albiflorum, R. arborescens, R. atlanticum, R. austrinum, R. canadense, R. canescens, R. catawbiense, R. columbianum, R. cumberlandense, R. eastmanii, R. flammeum, R. groenlandicum, R. lapponicum, R. macrophyllum, R. maximum, R. minus, R. occidentale, R. periclymenoides, R. prinophyllum, R. prunifolium, R. tomentosum, R. vaseyi, R. viscosum
Synonyms Azalea lapponica Azalea calendulacea
Name authority (Linnaeus) Wahlenberg: Fl. Lapp., 104. 1812 , (Michaux) Torrey: Fl. N. Middle United States, 425. 1824 ,
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