Rhododendron albiflorum
Rhododendron arborescens
Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron
smooth azalea, sweet azalea
bark ± smooth to furrowed;
twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy.
bark smooth to vertically furrowed, shredding;
twigs glabrous or, very rarely, sparsely, widely scattered, unicellular and multicellular eglandular-hairy.
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.
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).
lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered;
bracts similar to bud scales.
3–7-flowered;
bracts similar to bud scales.
to 9–15 mm, eglandular- and stipitate-glandular-hairy.
6–21 mm, glabrous or stipitate-glandular-hairy, sometimes also unicellular-hairy.
± 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.
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.
borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and unicellular-hairy.
borne on erect pedicels, 8–17 × 4.5–8 mm, ± densely multicellular stipitate-glandular-hairy, sometimes also sparsely unicellular-hairy.
with distinct tails;
testa closely appressed.
without distinct tails;
testa not dorsiventrally flattened, usually ± loose.
bud scales stipitate-glandular- and eglandular-hairy abaxially, margins stipitate-glandular-hairy.
bud scales usually glabrous abaxially, margins unicellular-ciliate.
= 26.
= 26.
Rhododendron albiflorum
Rhododendron arborescens
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.)
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.)
BC
OR
WA
Flora NW
PNW Herbaria
WildflowerSearch
iNaturalist
USDA Plants Database
MD Biodiversity
