Flora of the Southeastern United States
2022 Edition

Colors

Data mode

Key to Rhododendron

1 Leaves evergreen, coriaceous, entire; [rhododendrons and Labrador-tea].
..2 Leaves densely hairy beneath; petals separate
..2 Leaves either glabrous beneath or punctate with brown scales; petals fused.
....3 Lower surface of leaves not punctate with brown scales; larger leaves 10-30 cm long; [subgenus Hymenanthes, section Ponticum, subsection Pontica].
......4 Leaves rounded at base (rarely broadly cuneate or slightly cordate), obtuse at apex; leaf generally 1.5-2.5× as long as wide; corolla usually deep pink to purple; sepals 0.5-1 mm long
......4 Leaves cuneate at base, acute at apex; leaf generally 3-5× as long as wide; corolla usually white to pale pink; sepals 4-6 mm long
....3 Lower surface of leaves punctate with brown scales; larger leaves 6-12 cm long; [subgenus Rhododendron, section Rhododendron, subsection Caroliniana].
........5 Narrow part of the corolla tube ca. 0-2mm long; peak flowering simultaneous with peak flowering of Kalmia latifolia; [restricted to the Great Smoky Mountains, TN and NC]
........5 Narrow part of the corolla tube > 4 mm long; main flowering before to simultaneous with Kalmia latifolia; [FL, AL, GA, TN, SC, and NC].
..........6 Leaf apices mostly obtuse to rounded; leaves mostly 4.5-6.0 cm long, 1.7-2.4 cm wide, in the sun clearly revolute; petioles 2-6 (-7) mm long; branches erect and rigid; seeds moderately to elaborately ornamented with flared protrusions at both ends; [n. FL]
..........6 Leaf apices mostly acute to acuminate; leaves mostly 6-11 cm long, 2.0-4.0 cm wide, flat or only slightly revolute; petioles (5-) 6-20 mm long; branches spreading, not notably erect and rigid; seeds somewhat ornamented at one end; [c. GA northward].
............7 Corolla mostly 15-20 mm long, the corolla tube (9-13 mm long) shorter than to as long as the corolla lobes (12-18 mm long); plant flowering early relative to R. minus, despite often occurring at higher elevations and more northern latitudes, the main flowering in early spring, long before Kalmia latifolia; leaf growth starting with or after flowering; seeds ovoid, < 1.0 mm long, < 2.5× as long as wide (reminiscent of tiny watermelon seeds), coarsely textured, unornamented at the ends; calyx lobes deltoid; [mountain ridges, heath balds, and rocky summits, mostly either away from the Blue Ridge Escarpment or north of the Asheville Basin]
............7 Corolla mostly 25-37 mm long, the corolla tube (13-22 mm long) longer than the corolla lobes (8-12 mm long); plant flowering late relative to R. carolinianum, the main flowering in late spring, together with Kalmia latifolia; leaf growth before flowering (and in southern parts of the range also after flowering); seeds usually > 1.0 mm long, usually > 3× as long as wide, ornamented at one or both ends; calyx lobes ovate; [Coastal Plain, Piedmont, and Mountains, in the Mountains mostly of the Blue Ridge Escarpment of sw. NC and nw. SC, ranging up to the higher granitic domes in Macon and Jackson counties, NC].
1 Leaves deciduous, membranaceous, ciliate or serrulate; [azaleas, minniebush, and rhodora].
..............8 Corolla urceolate, the corolla lobes ca. 1 mm long; stamens 8; capsule 4-7 mm long, 4 (-5) locular; leaf mucro extremely prominent; midrib on lower leaf surface with a series of fascicles of glandular trichomes; [subgenus Azaleastrum, section Sciadorhodion]
..............8 Corolla tubular at the base, with well-developed flaring corolla lobes > 10 mm long (at least the lower); stamens either 5-7 or 10; capsule 7-25 mm long, 5-locular; leaf mucro not prominent; midrib on lower leaf surface variously pubescent, but not with a series of fascicles of glandular trichomes.
................9 Corolla tube 2-5 mm long or absent, much shorter than the corolla lobes; stamens (5-) 7 or 10; capsule ellipsoid-ovoid, 7-14 mm long; [subgenus Azaleastrum, section Sciadorhodion].
..................10 Corolla tube absent; stamens 10; leaves elliptic to obovate, < 3 cm wide, acute to rounded at the apex, the margin revolute; [PA and NJ northwards]
..................10 Corolla tube 2-5 mm long, much shorter than the corolla lobes; stamens (5-) 7; leaves elliptic, often broadly so (commonly 3-6 cm wide), acuminate, often with purplish coloration, the margin plane; [endemic in the s. Blue Ridge]
................9 Corolla tube 13-25 mm long, equal to or longer than the corolla lobes; stamens 5; capsule cylindroid-ellipsoid, 10-25 mm long; [subgenus Hymenanthes, section Pentanthera].
....................11 Outer (abaxial) surface of the vegetative bud scales densely pubescent; flowers appearing before or with the leaves (at least some of the leaves still folded or the vegetative bud scales still present) (except R. viscosum).
......................12 Capsule cylindroid, (3-) 4-5× as long as broad.
........................13 Corolla yellow-orange to orange-red; upper corolla lobe with a contrasting blotch; [s. GA west to se. MS]
........................13 Corolla white to pink; upper corolla lobe uniform in color (lacking a contrasting blotch); [collectively widespread in our area].
..........................14 Corolla tube narrow and somewhat abruptly expanding into the lobes, the lobes distinctly shorter than the tube; pedicels usually eglandular (occasionally glandular), (4-) 5-10 (-13) mm long; leaves inconspicuously ciliate, the cilia appressed to the leaf margin; capsule densely covered with nonglandular hairs; flowering Mar-May; [widely distributed from s. NC and n. TN southward]
..........................14 Corolla tube broader, gradually expanding into the lobes, the lobes about as long as or longer than the tube; pedicels usually glandular, (7-) 10-16 (-26) mm long; leaves conspicuously ciliate, the cilia diverging from the leaf margin; capsule glabrous or sparsely pubescent, the hairs at least partly gland-tipped; flowering May-Jun; [Mountains and upper Piedmont from n. NC (and rarely ne. AL) northward]
......................12 Capsule ovoid, 2-3 (-4)× as long as broad (if capsules absent, try both leads).
............................15 Corolla yellow-orange to orange-red; upper corolla lobe with a contrasting blotch; hairs of the capsule not gland-tipped; [Piedmont and Coastal Plain of GA and w. SC]
............................15 Corolla white to pink; upper corolla lobe uniform in color (lacking a contrasting blotch); hairs of the capsule gland-tipped (at least in part; nonglandular hairs also present); [collectively widespread in our area].
..............................16 Flowers appearing after the leaves have expanded (essentially all of the leaves unfolded, and the vegetative bud scales absent), typically May (Coastal Plain, low elevation, or south) to Aug (mountains, high elevation, or north)
................................17 Shrubs to 7 m tall; floral winter bud scales 15-20, at least the inner acute and aristate; corolla tube glabrous within, > 2× as long as the lobes; [primarily Coastal Plain]
................................17 Shrubs 1-2 (-5) m tall; floral winter bud scales 8-12 (-15), rounded (-mucronate) apically; corolla tube pubescent within, < 2× as long as the lobes; [more widespread]
..............................16 Flowers appearing before or with the leaves (at least some of the leaves still folded or the vegetative bud scales still present), typically Apr-May (unless stimulated by fire or weather).
..................................18 Leaf blade (3.2-) 3.4-4.7 (-5.2) cm long, (0.8-) 1.1-1.9 (-2.0) cm wide; plant typically strongly rhizomatous; [Coastal Plain from s. NJ south to sc. GA]
..................................18 Leaf blade (3.9-) 5.0-7.3 (-8.7) cm long, (1.2-) 1.8-3.0 (-3.7) cm wide; plant typically nonrhizomatous; [Mountains and upper Piedmont]
....................11 Outer (abaxial) surface of the vegetative bud scales glabrous or sparsely pubescent; flowers appearing before, with, or after the leaves.
....................................19 Capsule cylindric, (3-) 4-5 × as long as broad; flowers appearing before or with the leaves (at least some of the leaves still folded or the vegetative bud scales still present).
......................................20 Corolla white, with a contrasting yellowish blotch on the upper lobe; [se. TN and w. GA westward]
......................................20 Corolla deep pink (rarely white or nearly so), lacking a contrasting blotch on the upper lobe; [widespread in our area]
....................................19 Capsule ovate, 2-3.5× as long as broad; flowers appearing before, with, or after the leaves.
........................................21 Corolla white to pink (sometimes with yellow blotches).
..........................................22 Sepals 1.5-5 mm long; [primarily Appalachian: ne. PA and se. KY south to sc. NC, w. SC, c. GA, and c. AL]
..........................................22 Sepals 0.1-1 mm long; [collectively widespread].
............................................23 Leaves densely and softly pubescent beneath; [SC]
............................................23 Leaves glabrous beneath, except for strigose bristles along the midrib and major veins; [collectively widespread].
..............................................24 Shrubs to 7 m tall; floral winter bud scales 15-20, at least the inner acute and aristate; corolla tube glabrous within, > 2× as long as the lobes; [primarily Coastal Plain]
..............................................24 Shrubs 1-2 (-5) m tall; floral winter bud scales 8-12 (-15), rounded (-mucronate) apically; corolla tube pubescent within, < 2× as long as the lobes; [more widespread]
........................................21 Corolla predominantly yellow, orange, or orange-red.
................................................25 Flowers appearing before or with the leaves.
..................................................26 Floral bud-scales with glandular margins, the outer surface glabrous; corolla tube glandular-pubescent on its outer surface; sepals 2.0-3.0 mm long
..................................................26 Floral bud-scales with ciliate margins, the outer surface glabrous to sparsely pubescent; corolla tube pubescent (not glandular or rarely very weakly so) on the outer surface; sepals 0.5-3.0 mm long
................................................25 Flowers appearing after the leaves have expanded.
....................................................27 Twigs glabrous; [south of ec. AL and wc. GA]
....................................................27 Twigs pubescent with multicellular hairs; [e. KY and w. VA south to ec. TN, n. GA, and ne. AL; apparently disjunct in the Piedmont of SC]
......................................................28 Shrubs upright, not stoloniferous; corolla tube relatively wide, usually glandular-pubescent, yellow to orange or red; flower bud scales yellow-green (rarely with a brownish tinge)
......................................................28 Shrubs slightly to strongly stoloniferous; corolla tube relatively narrow, usually not glandular-pubescent, deep orange to red; flower bud scales brownish or at least brown-margined