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Rhododendron

See list of 12 species in this genus

Reference: Judd and Kron (2009).

  • 1a. Corolla apopetalous, white; capsules opening from base to apex; leaf blades densely white-tomentose on the abaxial surface, turning rusty-tomentose
  • 1b. Corolla gamopetalous, white to purple, often spotted or striped [Figs. 619,620]; capsules opening from apex to base; leaf blades variously scaly, scurfy, or pubescent on the abaxial surface, but not white- or rusty-tomentose
    • 2a. Leaf blades lepidote, especially on the abaxial surface; ovary lepidote
    • 2b. Leaf blades not lepidote; ovary glabrous or pubescent with eglandular and/or glandular hairs, but not lepidote
      • 4a. Leaves coriaceous, persistent and living throughout the year, the blade (8–) 10–20 cm long, eciliate; sepals 2–6 mm long (0.5–1.7 mm long in R. catawbiense)
        • 5a. Leaf blades cuneate at base, acute at apex, mostly 3–5 times as long as wide; sepals 2–6 mm long; corolla usually largely white or pale pink
        • 5b. Leaf blades rounded at base (infrequently cuneate or subcordate), obtuse at the apex, mostly 1.5–2.5 times as long as wide; sepals 0.5–1.7 mm long; corolla usually largely pink to purple
      • 4b. Leaves membranaceous, deciduous, the blade 2–10 (–12) cm long, ciliate along the margin (sometimes eciliate in R. vaseyi); sepals 0.1–1.1 mm long
        • 6a. Corolla strongly zygomorphic, divided into 3 portions—the upper portion 3-lobed, the 2 lower portions narrow and unlobed [Fig. 619]; flowers with 10 stamens; styles 1.5–2 cm long; capsules puberulent, sparsely, if at all, setose
        • 6b. Corolla weakly zygomorphic [Fig. 620]; flowers with 5–7 stamens; styles longer than 2 cm; capsules glabrous, evidently strigose-setose, or stipitate-glandular
          • 7a. Corolla yellow to orange-red to dark red, often with a prominent yellow blotch on the uppermost petal
            • 8a. Corolla with a funnel-shaped basal, connate portion, eglandular on the abaxial (i.e., outside) surface, the yellow blotch divided into smaller dots by veins; branchlets glabrous (infrequently sparsely pubescent)
            • 8b. Corolla with a nearly cylindrical basal, connate portion, stipitate-glandular on the abaxial surface, the yellow blotch (when present) not divided into smaller dots; branchlets pubescent
          • 7b. Corolla white to pink, unmarked or with red, brown, or green spots in R. vaseyi
            • 9a. Basal corolla tube 2–5 mm long, up to 25% as long as the lobes, glabrous on the abaxial (i.e., outside) surface; flowers with (5–) 7 stamens; fruit glabrous or with a few stipitate glands
            • 9b. Basal corolla tube 13–30 mm long, as long as or longer than the lobes, pubescent or stipitate-glandular on the abaxial surface; flowers with 5 stamens; fruit setose or stipitate-glandular or both
              • 10a. Flowers appearing after the expansion of the leaves, present June through July; corolla white (rarely pink); mature leaf blades (1.5–) 2–6 cm long, glabrous on the abaxial surface except for appressed strigae along the midrib and sometimes also the principal veins; pedicels stipitate-glandular
              • 10b. Flowers appearing before or with the expansion of the leaves, present May through June; corolla light to bright pink (rarely white); mature leaf blades (3–) 5–8 (–10) cm long, either softly pubescent across the surface or with strigae confined the major veins; pedicels with or without stipitate glands
                • 11a. Ovary, pedicels, and capsules stipitate-glandular [Fig. 620]; outer scales of vegetative winter buds pubescent on the abaxial surface, especially near the midvein; leaf blades permanently soft-pubescent on the abaxial surface, often also with strigae along the midrib
                • 11b. Ovary, pedicels, and capsules strigose with eglandular hairs; outer scales of vegetative winter buds ± glabrous (though ciliate on the margin); leaf blades glabrous on the abaxial surface except for appressed strigae along the midrib and sometimes also the principal veins

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