The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

Florida azalea, orange azalea

flame azalea

Habit Shrubs or trees, to 3(–5) m, usually not rhizomatous. Shrubs or trees, to 4(–10) m, usually not rhizomatous.
Stems

bark smooth to vertically furrowed, shredding;

twigs conspicuously multicellular stipitate-glandular-hairy, otherwise ± moderately to densely unicellular-hairy.

bark smooth to vertically furrowed, shredding;

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

Leaves

deciduous;

petiole multicellular stipitate-glandular-hairy and unicellular-hairy;

blade ovate to obovate, 3–11 × 1.5–4.5 cm, thin, membranous, margins entire, plane, ciliate, eglandular- and stipitate-glandular-hairy, apex acute to obtuse, often mucronate, abaxial surface ± moderately unicellular-hairy, adaxial surface sparsely scattered stipitate-glandular-hairy, otherwise ± moderately unicellular-hairy, rarely glabrescent.

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

9–24-flowered;

bracts similar to bud scales.

5–9-flowered;

bracts similar to bud scales.

Pedicels

5–17 mm, stipitate-glandular-hairy, otherwise ± densely unicellular-hairy.

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

Flowers

opening before or with leaves, erect to horizontal, slightly or not fragrant;

calyx lobes 0.5–2.5 mm, scattered stipitate-glandular-hairy, otherwise unicellular-hairy, margins long stipitate-glandular-hairy;

corolla yellow to orange, with usually red or orange-red tube, with indistinct, darker yellow, orange, or red blotch on upper lobe, funnelform, 25–45 mm, scattered stipitate-glandular-hairy, otherwise ± moderately unicellular-hairy on outer surface, petals connate, lobes 9–20 mm, tube ± gradually expanded into lobes, 15–25 mm (longer than lobes);

stamens 5, much exserted, ± unequal, 52–77 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.

Capsules

borne on erect pedicels, 14–26 × 3–5.5 mm, sparsely to densely stipitate-glandular-hairy, otherwise moderately to densely 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, flattened portion of testa well developed at each end;

testa expanded, dorsiventrally flattened, ± loose.

without distinct tails, flattened portion of testa well developed at each end;

testa expanded, dorsiventrally flattened, ± loose.

Floral

bud scales densely to moderately unicellular-hairy abaxially, margins unicellular-ciliate, also partly glandular-serrate.

bud scales usually glabrous abaxially, margins glandular.

2n

= 26.

= 52.

Rhododendron austrinum

Rhododendron calendulaceum

Phenology Flowering spring. Flowering spring–summer.
Habitat Wooded slopes, bluffs or lowlands along streams Mixed deciduous forests
Elevation 0-100 m (0-300 ft) 200-1000 m (700-3300 ft)
Distribution
from FNA
AL; FL; GA; MS
[WildflowerSearch map]
[BONAP county map]
from FNA
GA; KY; MD; NC; OH; PA; SC; TN; VA; WV
[WildflowerSearch map]
[BONAP county map]
Discussion

Rhododendron austrinum is most closely related to R. luteum Sweet of eastern Europe, Turkey, and the Caucasus region and to R. occidentale (K. A. Kron 1993).

(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. 466. 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. calendulaceum, 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
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 austrina Azalea calendulacea
Name authority (Small) Rehder: in L. H. Bailey, Stand. Cycl. Hort. 6: 3571. 1917 , (Michaux) Torrey: Fl. N. Middle United States, 425. 1824 ,
Web links