A deciduous azalea up to 6 ft high; young shoots finely downy and bristly. Leaves obovate, oval, or oblong, 11⁄2 to 21⁄2 in. long, half as much wide; upper surface bristly, lower one finely downy with bristles on the midrib; margins bristly; stalk 1⁄/6 in. long. Flowers opening in April and May, up to as many as fifteen in a truss. Corolla funnel-shaped, about 13⁄4 in. long, the tube slender, cylindric, and downy outside; scarlet or bright red with an orange-coloured blotch on the upper lobe. Stamens five, 2 in. long, downy below the middle. Ovary clothed with bristly, not glandular hairs; style 2 in. or more long, downy at the base. Calyx with five very small, ciliate, ovate, or oblong lobes. Flower-stalks bristly. (s. Azalea ss. Luteum)
Native of the S.E. United States from Georgia to S. Carolina. This, the most brilliantly coloured of all American azaleas, was in cultivation as long ago as 1789, and was figured in the Botanical Magazine in 1792 (t. 180). Old plants may still be in gardens, but the name appears to have been lost. It was in cultivation at Kew in 1881 as 'Azalea nudiflora coccinea'. Plants were sent to England by Professor Sargent in 1916. It has been confused with R. calendulaceum, but differs in the slender corolla-tubé which is not glandular as it is in that species. The flowers also are more numerous in the truss, and the colour 'is always scarlet or bright red and never varies to yellow' (Rehder). R. calendulaceum is a more northern shrub and hardier, but, as may be gathered from what is stated above, R. flammeum is quite hardy in this country. No doubt many of our richest- coloured deciduous azaleas owe much of their vivid red and scarlet hues to this species.