Rhododendron calendulaceum (Michaux) Torrey. Phen: May-Jun; Jun-Sep. Hab: Deciduous forests, particularly on mountain slopes, grassy balds. Dist: Largely Appalachian: s. PA and s. OH to c. GA and e. TN.
Origin/Endemic status: Endemic
Taxonomy Comments: This is a tetraploid species; various theories have been advanced about the origin of this polyploid chromosome complement. Kron (1993) argues that the evidence best fits an allopolyploid derivation of R. calendulaceum, involving hybridization between ancestors of R. cumberlandense and R. prinophyllum. Late-flowering, high elevation "orange azaleas", sometimes referred to as the "high altitude, late phase of Flame Azalea" are poorly understood and need additional study, but appear to belong here rather than with R. cumberlandense.
Synonymy: = C, F, FNA8, G, K1, K3, K4, NE, NY, Pa, RAB, Tn, Va, W, WV, Horn (2019), Kron (1993), Luteyn et al (1996), Wilson & Rehder (1921), Zhou et al (2008); = Azalea calendulacea Michx. – S