Distribution
Georgia, Greece, Russian Federation, Slovenia, Turkey, Ukraine

Caucasus, Balkans, Turkey, and isolated populations in Austria, Poland, Belarus, Ukraine, and Slovenia. Open wooded slopes, along streams and in swampy areas, shores of the Black Sea. Elevation: sea level to 2300 m. (Kron 1993, Orlov & Iakushenko 2017, GBIF.org)
Rhododendron luteum exhibits a typical Tertiary relict distribution in Europe (Szafer, 1975).
Species with high ecological plasticity, Rh. luteum forms dense understory in mixed forests with the dominance of Quercus petrea and Pinus sylvestris.

GBIF.org (3rd February 2018) GBIF Occurrence Download https://doi.org/10.15468/dl.b5mjq7

Shrub or small tree to 2-2.5 m tall, usually non-rhizomatous; young twigs red-brown, rarely yellowbrown, densely covered with unicellular hairs and multicellular gland-tipped hairs, rarely also with multicellular eglandular hairs, or with only multicellular gland-tipped and eglandular hairs. Vegetative bud scales glabrous, rarely sparsely covered with unicellular hairs abaxially; margin glandular ciliate. Leaf blade membranaceous, ovate or obovate to elliptic, (6.4-)7.6-12.0(-14.6) x (1.6-)2.1-3.4(-4.2) cm; base acute to oblique; apex acute to obtuse, often mucronate; adaxial surface sparsely to densely covered with multicellular gland-tipped hairs, or rarely with multicellular eglandular hairs, the midvein densely covered with unicellular hairs; abaxial surface glabrous, occasionally glaucous, the veins raised and prominent beneath, rarely sparsely to densely covered with unicellular hairs, or with multicellular gland-tipped and eglandular hairs, or all three types of hairs, the midvein sparsely to densely covered with unicellular and multicellular gland-tipped hairs, rarely lacking the unicellular hairs; margin entire, ciliate with multicellular eglandular hairs above and gland-tipped hairs below; petiole 0.3-0.6(-0.8) cm long, densely covered with unicellular hairs and multicellular gland-tipped hairs, rarely with multicellular eglandular and glandular hairs. Flower bud scales chestnut brown; abaxial surface glabrous, occasionally sparsely to densely covered with unicellular hairs; margin glandular. Flowers appearing before or with the leaves; inflorescence a shortened raceme of 9 to 17 flowers. Pedicels (0.8-)0.9-1.8(-2.4) cm long, densely covered with multicellular gland-tipped hairs, occasionally with unicellular hairs and multicellular gland-tipped hairs. Sepals less than 0. l-0.4(-0.7) cm long, varying in length on the same flower; margins glandular-fimbriate; abaxial surface sparsely covered with multicellular gland-tipped hairs, occasionally with unicellular hairs, rarely glabrous. Corolla yellow with a darker yellow blotch on the upper corolla lobe, fragrance sweet, the tube longer than the limb and gradually expanding into it; upper corolla lobe (1.3-)1.4-2.0(-2.4) x (0.8-)0.9-1.5(-2.0) cm wide; lateral lobes (1.3-)1.6-2.2(-2.5) x (0.5-)0.7-l.l(-1.2) cm; corolla tube (1.2-) 1.3-2.0(-2.4) cm long, 0.2-0.4(-0.5) cm wide at base; outer surface of corolla sparsely to densely covered with multicellular gland-tipped hairs, or also with unicellular hairs, the gland-tipped hairs continuing up the corolla lobes; inner surface of corolla glabrous", rarely sparsely covered with unicellular hairs. Stamens (3.2-)3.4-4.4(-5.0) cm long, with dense terete or flattened unicellular hairs on proximal (1.6-)1.7-2.3(-2.5) cm of filament, exserted (1.4-)1.8-2.7(-3.0) cm beyond throat of corolla. Style (3.5-)3.7-5.0(-5.4) cm long, exserted (2.2-)2.4-3.8 M.2) cm beyond throat of corolla, with dense unicellular hairs on proximal 0.2-0.6(-l .0) cm of style; stigma 0. l-0.2 cm wide. Ovary (0.2-)0.3-0.4 cm long, (0.1-)0.2-0.3 cm wide at the base, sparsely covered with multicellular hairs, often with flattened or terete unicellular hairs in a tuft at the apex. Capsules (1.3-) 1.5-2.1 (-2.2) x 0.4-0.7(-0.8) cm, broadly ovate, sparsely covered with unicellular hairs and sparsely to moderately covered with multicellular gland-tipped hairs. Seeds pale to dark chestnut brown,ovate or elliptic to fusiform,(2.4-)2.8-3.8 M.8) x (0.5-)0.7-1.2(-1.5) mm, body(l.l-)1.3- 1.8(-2.0) x (0.3-)0.4-0.6(-0.7) mm; testa expanded and dorsiventrally flattened, surrounding the body, the cells elongate, with tapered end-walls (Kron 1993). Chromosome number: In = 26 (Sax, 1930; Janaki-Ammaletal., 1950). See figures in Duhamel de Monceau, 1812; Galle, 1985.
Rhododendron luteum is most closely related to R. austrinum from which it can be distinguished by its broader, more glabrous fruits and its entirely yellow corolla with a deeper yellow blotch on the upper corolla lobe. The most noticeable difference between R. luteum and R. austrinum is the shape of the testa cells. Rhododendron luteum possesses seeds with elongate testa cells with tapered end-walls, whereas R. austrinum possesses seeds with short testa cells with transverse end-walls.
It is variable primarily in leaf shape and unicellular indumentum of the floral bud scales.