Rhododendron calendulaceum (flame azalea)

Plate 1 figs. a–h · 8 separate observations

Rhododendron calendulaceum, photographed by Christine Braaten — fig. a Christine Braaten, CC0 1.0 / 2022-06-04 / obs. 204987805

Rhododendron calendulaceum, photographed by Laura Gaudette — fig. b Laura Gaudette, CC BY 4.0 / obs. 200141982

Rhododendron calendulaceum, photographed by Michael J. Papay — fig. c Michael J. Papay, CC BY 4.0 / obs. 198602151

Rhododendron calendulaceum, photographed by Derek Hennen — fig. d Derek Hennen, CC BY 4.0 / obs. 201689919

Rhododendron calendulaceum, photographed by Siddarth Machado — fig. e Siddarth Machado, CC BY 4.0 / obs. 147268162

Rhododendron calendulaceum, photographed by Johanan Daniel — fig. f Johanan Daniel, CC BY 4.0 / obs. 143768085

Rhododendron calendulaceum, photographed by Craig Martin — fig. g Craig Martin, CC0 1.0 / obs. 139987607

Rhododendron calendulaceum, photographed by Will Kuhn — fig. h Will Kuhn, CC BY 4.0 / obs. 138735977

Every figure is a research-grade observation under CC0, CC BY or CC BY-SA, rehosted with the photographer’s name, the licence and the observation it came from. Photographs under a NonCommercial licence are excluded from this site and are never stored, which costs us a great many pictures and is not negotiable.

Native range 12 botanical countries

Native distribution of Rhododendron calendulaceum, after Kew’s World Checklist of Vascular Plants. Introduced, extinct and doubtful records are excluded, so this is where the plant is from, not everywhere it now grows.

Region	TDWG code	Continent
Alabama	ALA	NORTHERN AMERICA
Georgia	GEO
Kentucky	KTY
Maryland	MRY
New York	NWY
North Carolina	NCA
Ohio	OHI
Pennsylvania	PEN
South Carolina	SCA
Tennessee	TEN
Virginia	VRG
West Virginia	WVA

Region boundaries approximated from Natural Earth (public domain) and mapped to TDWG World Geographical Scheme for Recording Plant Distributions (WGSRPD) level-3 botanical countries (Brummitt 2001). Indicative, not the official WGSRPD geometry.

Flowering 721 in flower of 740 examined

96%

98%

100%

Proportion of examined Rhododendron calendulaceum in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	1	1	too few examined
Feb	0	0	too few examined
Mar	2	2	too few examined
Apr	97	101	96%	90% to 98%
May	258	264	98%	95% to 99%
Jun	317	325	98%	95% to 99%
Jul	40	41	98%	87% to 100%
Aug	6	6	100%	61% to 100%
Sep	0	0	too few examined
Oct	0	0	too few examined
Nov	0	0	too few examined
Dec	0	0	too few examined

Peak flowering in Aug. Each bar is the share of Rhododendron calendulaceum observations in which someone actually recorded the reproductive state and found the plant in flower, not the raw number of flowering records. That distinction matters: people observe plants far more in spring than in winter, so a bare count of flowering records partly measures when people go outside. Dividing by the number examined removes that. 721 of 740 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 7 months have fewer than 5 examined observations, so no proportion is drawn for them. This is still a global aggregate and not a forecast for your garden: the same species flowers on different dates in different hemispheres. Where a species has fewer than 30 flowering records we do not draw this chart at all. Computed from 10.15468/dl.cgje2x.

Where it actually grows measured, from 1,955 observations

Condition	5th percentile	Median	95th percentile
Coldest month, mean daily low	-7.6 °C	-3.3 °C	0.8 °C
Warmest month, mean daily high	20.7 °C	26.3 °C	30.6 °C
Annual rainfall	1,081 mm	1,518 mm	2,042 mm
Rainfall in the driest quarter	226 mm	311 mm	436 mm

It is found where winters bring hard frost. This is not care advice and it is not a forecast. It is a measurement: we sampled the climate at every one of the 1,955 research-grade observations of Rhododendron calendulaceum that carry a coordinate, and this is the range those places actually span. The 5th and 95th percentiles are used rather than the minimum and maximum, because a single cultivated specimen in a heated conservatory should not widen a tropical plant's range to the Arctic.

This is not a hardiness zone. A USDA zone is the average annual extreme minimum temperature. The figure above is the mean daily minimum of the coldest month, which is a different quantity and is typically far warmer. Reading one as the other would place a plant several zones too warm, so we do not publish a hardiness zone, because we do not have one. Climate from CHELSA V2.1 (Karger et al. 2017); occurrences from 10.15468/dl.cgje2x.

Also published as 14 synonyms

A synonym is not an error. It is a record of botanists disagreeing, in print, about where this plant belongs. Each of these was somebody’s considered answer.

Azalea aurantiaca F.Dietr.
Azalea calendulacea Michx.
Azalea calendulacea var. crocea Michx.
Azalea conccinea Lodd.
Azalea crocea (Michx.) Hoffmanns.
Azalea jammea Pritz.
Azalea speciosa Willd.
Azalea speciosa var. aurantia (G.Lodd.) DC.
Azalea speciosa var. coccinea (Aiton) DC.
Rhododendron calendulaceum f. aurantium (F.Dietr.) Rehder
Rhododendron calendulaceum f. calendulaceum
Rhododendron calendulaceum var. croceum (Michx.) Sweet
Rhododendron luteum var. croceum (Michx.) C.K.Schneid.
Rhododendron speciosum (Willd.) Sweet

Sourcesevery claim on this page

World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.
Wikidata. common name (P1843), joined on the World Flora Online identifier (P7715). CC0. Retrieved 2026-07-13.
Kew, World Checklist of Vascular Plants (WCVP v16). native distribution by TDWG level-3 botanical country, and life form. CC BY 3.0. Retrieved 2026-06-04.

We publish what we can source and we say so when we cannot. This page has no care advice and no toxicity claim, because we do not yet have those from a source we can cite.