ERICACEAE: Heath Family
KEY TO SPECIES OF RHODODENDRON
1. Plant evergreen (GROUP H) …………………………………… 2
2. Leaf blade apex acute to acuminate; petiole averaging 6 mm or more; branches limber, mostly zigzag .......................... R. minus
2. Leaf blade apex usually obtuse; petiole averaging 5 mm or less; branches stiff, mostly straight ................................. R. chapmanii
1. Plants deciduous (GROUP J) ………………………. 3
3.Flowers appearing before or with leaves (at least some of the leaf blades still folded or some vegetative bud scales still present) ........................... 4
4. Corolla somewhat bell-shaped, base united 2-5 mm ............... R. vaseyi
4. Corolla elongated, base united 11-36 mm .................................... 5
5. Upper corolla lobe with contrasting blotch or spots, the blotch often appearing simply as darker in color area (sometimes slight) at lobe base ......................................................................... 6
6. Corolla yellow to orange or red, the limb nearly as broad as the tube is long, the tube abruptly expanding into the limb ..................... 7
7. Floral bud scales with glandular margins, corolla tube with abundant multicellular glandular hairs .................. R. calendulaceum
7. Floral bud scales with ciliate margins, corolla tube with abundant multicellular glandless hairs, occasionally very weakly glandular ..................................................... R. flammeum
6. Corolla white or yellow to orange, the limb shorter than the length of the tube, the tube gradually expanding into the limb ……………………………. 8
8. Corolla yellow to orange, sometimes with dark pink or red; floral bud scale margin glandular ......................... R. austrinum
8. Corolla white, with a contrasting yellow blotch on the upper lobe; floral bud scale margin ciliate ................... 9
9. Flowers opening before the leaves have expanded; flower buds with non-glandular margins ...................... R. alabamense
9. Flowers opening after the leaves have expanded; flower buds with margins glandular along their lower 2/3s ...................................................................................................... R. eastmanii
5. Upper corolla lobe the same color as the other lobes, without a visible contrasting or darker blotch ............................................ 10
10. Plants low-growing and strongly rhizomatous. Multicellular glandular hairs on corolla tube forming lines that continue along outer surface of the lobes; corolla white, tube equal to or longer than the distance stamens extend beyond the corolla .................... R. atlanticum
10. Plants usually tall and not strongly rhizomatous. Multicellular glandular or glandless hairs scattered on outerside of corolla tube, neither forming distinct lines nor continuing up the lobes; corolla pink to white, tube shorter than the distance stamens extend beyond the corolla .......................................................11
11. Corolla pink, covered with multicellular glandless hairs............................ R. periclymenoides
11. Corolla pink, or pink and white, covered with multicellular glandular hairs .................................... 12
12. Leaf blade glabrous or with only sparse unicellular hairs. Floral bud scales glabrous; pedicel and sepal margin usually glandless with pedicel often lacking unicellular hairs or only sparsely covered with them ......................... R. periclymenoides
12. Leaf blade underside with moderate to abundant unicellular hairs. Floral bud scales covered with unicellular hairs; pedicel and sepal margin with or without glands; pedicel usually covered with unicellular hairs ............................................ 13
13. Leaf blade inconspicuously ciliate, the hairs appressed to blade margin. Pedicel usually glandless and relatively short, occasionally glandular. Corolla tube narrow and somewhat abruptly expanding into the limb ............ R. canescens
13. Leaf blade conspicuously ciliate, the hairs ascending away from blade margin. Pedicel usually glandular and relatively long. Corolla tube broader and gradually expanding into the limb .................................... R. prinophyllum
3. Flowers appearing after the leaves have expanded (essentially all of the leaves unfolded and vegetative bud scales absent) ................................... 14
14. Stems glabrous ........................................................... 15
15. Corolla coral-orange or salmon to deep red ............ R. prunifolium
15. Corolla white .......................................... R. arborescens
14. Stems with multicellular hairs (glandular or glandless) and/or unicellular hairs ............................................... 16
16. Corolla yellow to orange and red, with a blotch or darker spot on the upper lobe, tube abruptly expanding into the lobes; floral bud scale margin glandular, the outerside glabrous .................... R. cumberlandense
16. Corolla white or occasionally pink but always lacking a blotch on the upper lobe, tube gradually expanding into the lobes; floral bud scale margin usually ciliate, occasionally also mixed with glands and unicellular hairs, outerside glabrous to profusely unicellular-hairy ……….. R. viscosum