A deciduous shrub of vigorous, rather stiff habit, 8 to 10 ft high; young shoots viscous, glandular. Leaves linear-oblong, 21⁄2 to 5 in. long, 3⁄4 to 11⁄2 in. wide;with a short, abrupt tip, more tapering at the base; at maturity glaucous, hairy beneath along the midrib and at the margins; stalk hairy, 1⁄3 in. or less long. Flowers fragrant, rich bright yellow, 11⁄2 to 2 in. across, crowded in several clusters at the end of the previous year's naked shoots, in May, on sticky, glandular stalks 1⁄2 to 3⁄4 in. long. Calyx-lobes small, ovate, edged with glanded hairs. Corolla-tube 1⁄2 in. long, hairy. Stamens five, hairy at the base like the style. Bot. Mag., t. 433. (s. Azalea ss. Luteum)
Native mainly of the western Caucasus, where it grows from sea-level to the subalpine zone, and of bordering parts of Turkey. In Russia it is also found in the N.W. Ukraine and bordering parts of White Russia, and there is an isolated stand under State protection in Poland (Wola Zarczycka, near Lezaysk). Outposts have also been reported from E. Austria and N.W. Yugoslavia. It was introduced to Britain from the Caucasus by Pallas in 1792 to Lee and Kennedy's nursery and again by Anthony Hove of Warsaw in 1796.
This beautiful perfectly hardy azalea, the only yellow one known until the advent of R. molle (sinense), and the parent or the predominant parent of all the older yellow garden varieties, is still one of the most useful and generally cul tivated of all shrubs. It blossoms unfailingly, and with an exquisite fragrance. Added to this is its fine autumn colouring, in shades of red, orange and purple. Coming freely from seed, it is the chief stock used for grafting the choicer varieties on. This probably explains its abundance in gardens, for being a vigorous grower it will, unless watched, often send up strong sucker growths that in time smother out the more finely bred sorts grafted on it.
R. luteum produces thickets of self-sown seedlings when grown in grass-free undisturbed soils and has become semi-naturalised in some localities. It is of great phytogeographic interest as the only European azalea, belonging to a subseries which has its headquarters in N. America, but represented in E. Asia also.
From the Supplement (Vol. V)
In Asiatic Turkey this species is not confined to the north-east: it is fairly widespread along the northern ranges and in western Anatolia. It also occurs, or did, on the Greek islands of Lesbos and Samos.