Rhododendron albiflorum
Rhododendron calendulaceum
Cascade azalea, white rhododendron, white-flower azalea, white-flower rhododendron
flame azalea
bark ± smooth to furrowed;
twigs multicellular eglandular-hairy (hairs unbranched) and unicellular-hairy.
bark smooth to vertically furrowed, shredding;
twigs sparsely to conspicuously multicellular eglandular-hairy (hairs unbranched), otherwise sparsely to moderately unicellular-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 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.
lateral (axillary, i.e., above leaf scars, spaced along shoots of previous year), fasciculate, 1–2-flowered;
bracts similar to bud scales.
5–9-flowered;
bracts similar to bud scales.
to 9–15 mm, eglandular- and stipitate-glandular-hairy.
7–14 mm, stipitate-glandular-hairy and/or eglandular-hairy, otherwise sparsely to densely 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 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.
borne on erect pedicels, 6–8 × 5–6 mm, stipitate-glandular-, eglandular-, and 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.
with distinct tails;
testa closely appressed.
without distinct tails, flattened portion of testa well developed at each end;
testa expanded, dorsiventrally flattened, ± loose.
bud scales stipitate-glandular- and eglandular-hairy abaxially, margins stipitate-glandular-hairy.
bud scales usually glabrous abaxially, margins glandular.
= 26.
= 52.
Rhododendron albiflorum
Rhododendron calendulaceum
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 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.)
BC
OR
WA
Flora NW
PNW Herbaria
WildflowerSearch
iNaturalist
USDA Plants Database
MD Biodiversity
