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Rhododendron calendulaceum (Michx.) Torr.

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Kindly sponsored by
Peter Norris, enabling the use of The Rhododendron Handbook 1998

Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Rhododendron calendulaceum' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/rhododendron/rhododendron-calendulaceum/). Accessed 2024-09-19.

Genus

Synonyms

  • Azalea calendulacea Michx.

Infraspecifics

Other taxa in genus

Glossary

corolla
The inner whorl of the perianth. Composed of free or united petals often showy.
bud
Immature shoot protected by scales that develops into leaves and/or flowers.
calyx
(pl. calyces) Outer whorl of the perianth. Composed of several sepals.
clone
Organism arising via vegetative or asexual reproduction.
corolla
The inner whorl of the perianth. Composed of free or united petals often showy.
glandular
Bearing glands.
midrib
midveinCentral and principal vein in a leaf.

Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Rhododendron calendulaceum' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/rhododendron/rhododendron-calendulaceum/). Accessed 2024-09-19.

Rhododendron calendulaceum

Rhododendron calendulaceum Simmons & Elsley 62, collected in the Great Smoky Mountains, Tennesssee, in 1980, flourishing in Ray Wood, Castle Howard, North Yorkshire, UK, June 2018. Image John Grimshaw.

Deciduous shrub or small tree, to 10 m; young twigs densely eglandular-hairy. Leaves (4.5–)5.5–7(–9) × (1.3–)1.8–2.6(–3.3) cm, ovate or obovate to elliptic, with lamina glabrous or covered with eglandular hairs. Flower bud scales with outer surface usually glabrous though rarely sparsely covered with unicellular hairs. Pedicels covered with gland-tipped and/or eglandular hairs. Flowers with an acrid fragrance, appearing before or with the leaves, 5–9, in a shortened raceme; calyx 1–3 mm; corolla orange to flame red, funnelform, tube abruptly expanding into the limb, 35–55 mm, outer surface of tube covered with unicellular and gland-tipped multicellular hairs. Capsules covered with unicellular hairs and eglandular or (less often) gland-tipped hairs. Flowering May-July. Royal Horticultural Society (1997)

Distribution  United States Appalachians

Habitat 180–1,000 m

RHS Hardiness Rating H6

Awards AM 1965 (Crown Estate Commissioners, Windsor) to a clone 'Burning Light'; flowers coral red, with orange throats. AM 1989 (Crown Estate Commissioners, Windsor) to a clone 'Amber Light'; trusses with up to 10-12 flowers; corolla with shades of orange darkening to red in throat and on lobes.

Conservation status Least concern (LC)

Taxonomic note This species is closely allied to R. flammeum but is distinguished by its glandular flower bud scales and more densely glandular corolla tube. Royal Horticultural Society (1997)

A deciduous shrub up to 10 or more feet high; young shoots bristly-hairy. Leaves obovate or oval, 2 to 4 in. long, 3⁄4 to 11⁄4 in. wide, with a few scattered hairs above, downy beneath, especially on the midrib and veins; leaf-stalk hairy, very short. Flowers of various shades of red, orange, and yellow, scarcely fragrant, produced in showy terminal clusters of five or more. Corolla-tube about 1⁄2 in. long, glandular-hairy; lobes often 1 in. long, often considerably longer than the tube; calyx-lobes edged with long, erect hairs; flower-stalk 1⁄4 in. long, glandular-hairy. Flowers in May or early June. (s. Azalea ss. Luteum)

Native of eastern N. America in the Alleghenies. This is the most brilliantly coloured of all wild azaleas, and is the source of the scarlet and orange-coloured garden hybrids. Bartram gives this description of his first sight of this azalea in the Carolina mountains: ‘I saw the blossoms covering plants on the hill-sides in such incredible profusion that, suddenly opening to view from deep shade, I was alarmed by the apprehension of the hill being on fire.’

R. calendulaceum was brought to England by John Lyon in 1806, but there may have been an earlier introduction, since the azalea named A. aurantiaca by Dietrich in 1803 came from England and was probably a form of this species.

A.M. 1965 to clone ‘Burning Light’, shown by the Crown Estate Commissioners.

Rhododendron calendulaceum

A paler flower colour among Rhododendron calendulaceum Simmons & Elsley 62, from the Great Smoky Mountains, Tennesssee (Ray Wood, June 2018). Image John Grimshaw.

Rhododendron calendulaceum

Rhododendron calendulaceum Simmons & Elsley 62 (Ray Wood, Castle Howard, June 2022) Image John Grimshaw.

Rhododendron calendulaceum

Massed planting of Rhododendron calendulaceum Simmons & Elsley 62 in fill flower in Ray Wood, Castle Howard, June 2024. Image John Grimshaw.

R bakeri (Lemmon & McKay) Hume

Synonyms
Azalea bakeri Lemmon & McKay
R. cumberlandense E. L. Braun

Allied to R. calendulaceum, but flowering about three weeks later and generally of dwarfer, more compact habit, rarely up to 9 ft high; said to be superior as an ornamental. Native mainly of the Cumberland plateau. See further in R.C.Y.B. 1957, pp. 20–1, 23.

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