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Piedmont rhododendron

Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron

Habit Shrubs, to 3(–5) mm, often rhizomatous. Shrubs, to 2.5 m, rhizomatous.
Stems

bark smooth to vertically furrowed, shredding;

twigs with ferrugineous, multicellular, broad-rimmed, glandular-peltate scales.

bark ± smooth to furrowed;

twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy.

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- and stipitate-glandular-hairy and unicellular-hairy;

blade narrowly elliptic or ovate to obovate, 2–9 × 0.8–3 cm, thin, membranous to chartaceous, margins minutely serrate, plane, ciliate when young, eglandular- and stipitate-glandular-hairy, apex acute to ± rounded, surfaces scattered eglandular-hairy, ± glabrescent.

Inflorescences

5–10-flowered;

bracts similar to bud scales.

lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered;

bracts similar to bud scales.

Pedicels

5–15 mm, with ferruginous scales.

to 9–15 mm, eglandular- and stipitate-glandular-hairy.

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.

± radially symmetric, opening soon after (and borne below) expanded leaves, pendulous, very fragrant (similar to vanilla and jasmine);

calyx lobes 5–17 mm, eglandular- and stipitate-glandular-hairy, margins glandular-hairy;

corolla white, rarely marked with yellow, bowl-shaped, 9–22 mm, minutely unicellular-hairy or glabrous on outer surface, petals connate, lobes 6–15 mm, tube expanding into lobes, 3–9 mm;

stamens 9(–12), included, ± unequal, 5.5–14 mm.

Capsules

borne on erect pedicels, 6–14 × 2.9–5 mm, with ferruginous, peltate scales.

borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy.

Seeds

with short, blunt/truncate tails at each end;

testa closely appressed.

with distinct tails;

testa closely appressed.

Floral

bud scales ferruginous-lepidote, sometimes also unicellular-hairy abaxially, margins unicellular-ciliate.

bud scales stipitate-glandular- and eglandular-hairy abaxially, margins stipitate-glandular-hairy.

2n

= 26.

= 26.

Rhododendron minus

Rhododendron albiflorum

Phenology Flowering late spring–summer.
Habitat Coniferous forests, alpine thickets, stream banks, seeps on rock outcrops
Elevation 800-3500 m (2600-11500 ft)
Distribution
from FNA
AL; FL; GA; NC; SC; TN
[WildflowerSearch map]
[BONAP county map]
from FNA
CO; ID; MT; OR; WA; AB; BC
[WildflowerSearch map]
[BONAP county map]
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 albiflorum is especially distinctive due to its axillary, white, somewhat pendulous, and nearly actinomorphic flowers, and it is placed in the monotypic subg. Candidastrum (Sleumer) Philipson & Philipson (W. R. Philipson and M. N. Philipson 1986). It is occasionally used as an ornamental. The disjunct population in Colorado has somewhat smaller calyx lobes and corollas and shorter stamens; it is sometimes recognized as var. warrenii (M. A. Lane et al. 1993). This variety is not recognized here because of the extent of morphological overlap between that population and those of the Pacific Northwest.

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

Key
1. Leaf blades: apex usually acute or acuminate; petioles (5-)6-20 mm; branches not rigidly ascending.
var. minus
1. Leaf blades: apex usually rounded or obtuse; petioles 2-6(-7) mm; branches usually rigidly erect-ascending
var. chapmanii
Source FNA vol. 8, p. 460. FNA vol. 8, p. 464.
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. occidentale, R. periclymenoides, R. prinophyllum, R. prunifolium, R. tomentosum, R. vaseyi, R. viscosum
R. alabamense, 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
Subordinate taxa
R. minus var. chapmanii, R. minus var. minus
Synonyms Azaleastrum albiflorum, R. albiflorum var. warrenii
Name authority Michaux: J. Hist. Nat. 1: 412. 1792 , Hooker: Fl. Bor.-Amer. 2: 43, plate 133. 1834 ,
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