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Rhododendron macrophyllum

big leaf rhododendron, California rhododendron, California rose bay, coast rhododendron, Pacific rhododendron, western rhododendron

Alabama azalea

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

bark smooth to vertically furrowed, shredding;

twigs with basally branched, crisped/matted, eglandular hairs, very quickly glabrate.

bark smooth to vertically furrowed, shredding;

twigs scattered, multicellular eglandular-hairy (hairs unbranched), otherwise glabrous or moderately unicellular-hairy.

Leaves

persistent;

petiole glabrous;

blade elliptic to slightly ovate or obovate, (6–)8.5–14(–20) × 2.5–5.5(–7.5) cm, thick, coriaceous, margins entire, plane to revolute, glabrous, apex acute to obtuse or slightly acuminate, surfaces scattered eglandular-hairy (hairs branched basally, crisped, very quickly deciduous), abaxial surface ± smooth.

deciduous;

petiole unicellular- and stipitate-glandular-hairy;

blade ovate to obovate, 4–7.7(–9.4) × 1.2–2.5(–3.3) cm, thin, membranous, margins entire, plane, ciliate, eglandular-hairy, apex acute to obtuse, often mucronate, abaxial surface glabrous or unicellular-hairy, adaxial surface usually scattered eglandular-hairy, usually also unicellular-hairy.

Inflorescences

10–20-flowered;

bracts similar to bud scales.

6–7-flowered;

bracts similar to bud scales.

Pedicels

30–60 mm, glabrous.

4–12 mm, eglandular- and/or stipitate-glandular-hairy, otherwise glabrous or moderately unicellular-hairy.

Flowers

opening after development of leaves (of flowering shoots), erect to horizontal, fragrant;

calyx lobes 1–1.5 mm, glabrous, except margins eglandular- and stipitate-glandular-hairy;

corolla white to pink or rose-purple, with yellowish green spots on upper lobe, broadly campanulate, 24–48 mm, outer surface glabrous, petals connate, lobes 14–30 mm, tube gradually expanding into lobes, 10–23 mm;

stamens 10, included, ± unequal, 16–37 mm.

opening before or with leaves, erect to horizontal, very fragrant;

calyx lobes 0.1–3 mm, scattered eglandular-hairy and/or stipitate-glandular-hairy, otherwise sparsely to moderately unicellular-hairy, margins eglandular-hairy;

corolla white, sometimes pink-tinged, with contrasting yellow blotch on upper lobe, funnelform, 25–42 mm, scattered stipitate-glandular-hairy (hairs often continuing in lines up lobes), otherwise sparsely to moderately unicellular-hairy on outer surface, petals connate, lobes 9–21 mm, tube usually ± gradually expanded into lobes, 15–31 mm (longer than lobes);

stamens 5, much exserted, ± unequal, 37–69 mm.

Capsules

borne on erect pedicels, 13–25 × 4–7 mm, eglandular-hairy (hairs ferruginous, branched or unbranched) and, often, stipitate-glandular-hairy.

borne on erect pedicels, 14–22 × 3–4 mm, sparsely to moderately multicellular eglandular-hairy, otherwise moderately to densely unicellular-hairy.

Seeds

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

testa expanded, dorsiventrally flattened, loose.

without distinct tails;

testa expanded, dorsiventrally flattened, ± loose.

Floral

bud scales multicellular eglandular-hairy (hairs branched basally), and unicellular-hairy (hairs short to elongate) abaxially, margins eglandular-hairy (hairs branched).

bud scales glabrous or glabrate abaxially, margins unicellular-ciliate.

2n

= 26.

= 26.

Rhododendron macrophyllum

Rhododendron alabamense

Phenology Flowering spring–summer. Flowering spring.
Habitat Forest and forest margins, thickets Open, dry woodlands, rocky slopes
Elevation 50-1600 m [160-5200 ft] 0-500 m [0-1600 ft]
Distribution
from FNA
CA; OR; WA; BC
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; FL; GA; MS; TN
[WildflowerSearch map]
[BONAP county map]
Discussion

Rhododendron macrophyllum, R. maximum, and R. catawbiense represent subg. Hymenanthes (Blume) K. Koch in North America; the subgenus is represented by hundreds of species in temperate eastern Asia and is characterized by its branched, eglandular hairs (D. F. Chamberlain 1982). These showy plants are frequently used as ornamentals.

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

Rhododendron alabamense may be most closely related to a clade containing orange-red-flowered species (K. A. Kron 1993). This species has sometimes been confused with R. eastmanii; R. alabamense flowers before or as the leaves expand whereas R. eastmanii flowers after the leaves have expanded. Hybrids with R. canescens are known.

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

Source FNA vol. 8, p. 462. Treatment authors: Walter S. Judd, Kathleen A. Kron. FNA vol. 8, p. 467. Treatment authors: Walter S. Judd, Kathleen A. Kron.
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. maximum, R. minus, R. occidentale, R. periclymenoides, R. prinophyllum, R. prunifolium, R. tomentosum, R. vaseyi, R. viscosum
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. occidentale, R. periclymenoides, R. prinophyllum, R. prunifolium, R. tomentosum, R. vaseyi, R. viscosum
Synonyms R. californicum Azalea alabamensis
Name authority D. Don ex G. Don: Gen. Hist. 3: 843. 1834 , Rehder: in E. H. Wilson and A. J. Rehder, Monogr. Azaleas, 141. 1921 ,
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