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California azalea, western azalea

smooth azalea, sweet azalea

Habit Shrubs or trees, to 8(–10) m, usually not rhizomatous. Shrubs or trees, to 6 m, usually not rhizomatous.
Stems

bark smooth to vertically furrowed, shredding;

twigs sparsely to densely multicellular stipitate-glandular-hairy or unicellular-hairy, or glabrous, sometimes only unicellular-hairy.

bark smooth to vertically furrowed, shredding;

twigs glabrous or, very rarely, sparsely, widely scattered, unicellular and multicellular eglandular-hairy.

Leaves

deciduous;

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

blade ovate or obovate to elliptic, (2.5–)3.5–8.2(–10.8) × 1.2–2.9(–3.6) cm, thin, membranous, margins entire, plane, ciliate, eglandular-hairy, sometimes also stipitate-glandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous or sparsely unicellular-hairy, often also stipitate-glandular-hairy (or, rarely, stipitate-glandular- and eglandular-hairy), adaxial surface sparsely scattered, multicellular eglandular- and/or stipitate-glandular-hairy and unicellular-hairy, or glabrous.

deciduous;

petiole glabrous or multicellular eglandular-hairy;

blade ovate to obovate, 3–8(–10.5) × 1.3–3.5 cm, thin, chartaceous, margins entire, plane, ciliate, eglandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous, (sometimes glaucous), adaxial surface glabrous, (lustrous).

Inflorescences

3–15-flowered;

bracts similar to bud scales.

3–7-flowered;

bracts similar to bud scales.

Pedicels

9–26 mm, stipitate-glandular- and, sometimes, also eglandular-hairy.

6–21 mm, glabrous or stipitate-glandular-hairy, sometimes also unicellular-hairy.

Flowers

opening with leaves or after they have expanded, erect to horizontal, fragrant or mephitic-scented;

calyx lobes 1–4(–9) mm, often stipitate-glandular- and/or eglandular-hairy, sometimes also unicellular-hairy, margins usually stipitate-glandular-hairy;

corolla white with contrasting yellow blotch on upper lobe, white and pink or salmon, or pink with orange blotch on upper lobe, rarely white with yellow lines at throat, or with tube white to red, funnelform, 30–58 mm, stipitate-glandular-hairy and, rarely, also eglandular-hairy, otherwise sparsely to moderately unicellular-hairy or these hairs absent on outer surface, petals connate, lobes 13–29 mm, tube gradually expanding into lobes, 15–29 mm (equaling or longer than lobes);

stamens 5, much exserted, ± unequal, 40–75 mm.

opening after leaves, erect to horizontal, very fragrant;

calyx lobes 0.8–6(–9) mm, surfaces and margins scattered, stipitate-glandular- and/or, sometimes, eglandular-hairy;

corolla white or, sometimes, light pink (contrasting with dark pink to red style and filaments), without blotch on upper lobe, funnelform, 30–55 mm, stipitate-glandular-hairy (hairs continuing in lines up lobes), otherwise glabrous or sparsely unicellular-hairy on outer surface, petals connate, lobes 10–24 mm, tube ± gradually expanded into lobes, 20–37 mm (equaling or much longer than lobes);

stamens 5, much exserted, ± unequal, 44–82 mm.

Capsules

borne on erect pedicels, 12–22 × 4–14 mm, multicellular stipitate-glandular-hairy, sometimes also eglandular-hairy, otherwise sparsely unicellular-hairy (unicellular hairs rarely absent).

borne on erect pedicels, 8–17 × 4.5–8 mm, ± densely multicellular stipitate-glandular-hairy, sometimes also sparsely unicellular-hairy.

Seeds

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

testa expanded, dorsiventrally flattened, ± loose.

without distinct tails;

testa not dorsiventrally flattened, usually ± loose.

Floral

bud scales sparsely to densely unicellular-hairy abaxially, rarely also sparsely eglandular- or stipitate-glandular-hairy, margins unicellular-ciliate, or with glands and cilia mixed, or glandular.

bud scales usually glabrous abaxially, margins unicellular-ciliate.

2n

= 26.

= 26.

Rhododendron occidentale

Rhododendron arborescens

Phenology Flowering spring–summer. Flowering late spring–summer.
Habitat Moist, wooded slopes and canyon bottoms, along streams, thickets, bogs, serpentine ridges, ocean bluffs Stream banks, rocky streamsides, heath balds, swampy woods or bogs
Elevation 0-2700 m (0-8900 ft) 90-1500 m (300-4900 ft)
Distribution
from FNA
CA; OR
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; GA; KY; MD; NC; PA; SC; TN; VA; WV
[WildflowerSearch map]
[BONAP county map]
Discussion

The flowers of Rhododendron occidentale show an exceptional range of variation in color.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Rhododendron arborescens is most closely related to R. viscosum, as evidenced by their glabrous floral bud scales and flowers that appear after the leaves have expanded (K. A. Kron 1993). It can be distinguished by its glabrous branchlets, red style and filaments (which contrast with the white corollas), and distinctive seeds that lack loose, expanded testae. These two species occasionally hybridize; hybrids with R. cumberlandense also are known.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 8, p. 467. FNA vol. 8, p. 470.
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. lapponicum, R. macrophyllum, R. maximum, R. minus, R. periclymenoides, R. prinophyllum, R. prunifolium, R. tomentosum, R. vaseyi, R. viscosum
R. alabamense, R. albiflorum, R. atlanticum, R. austrinum, 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
Synonyms Azalea occidentalis, Azalea californica, R. occidentale var. paludosum, R. sonomense Azalea arborescens
Name authority (Torrey & A. Gray) A. Gray: in W. H. Brewer et al., Bot. California 1: 458. 1876 , (Pursh) Torrey: Fl. N. Middle United States, 425. 1824 ,
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