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Subshrubs, shrubs, or trees, (rhizomatous or not). Stems erect (and/or creeping, prostrate in R. groenlandicum, R. lapponicum, R. tomentosum); twigs hairy or glabrous, (older twigs without peglike projections). Leaves persistent or deciduous, alternate; petiole present; blade coriaceous to membranous, (base cuneate, rounded, or obtuse), margins entire, (sometimes ciliate, plane to revolute, abaxial surface 1/3+ visible except sometimes in bud, surfaces hairy and/or scaled, midvein hairy or not, adaxial surface sometimes impressed; venation usually brochidodromous). ( Winter buds usually large, with imbricate scales; floral buds usually larger than vegetative buds.) Inflorescences terminal (axillary in R. albiflorum, short, corymbiform or rounded racemes (fasciculate racemes in R. canadense, R. lapponicum; fasciculate in R. albiflorum), 3-35-flowered (1-2-flowered in R. albiflorum); perulae brownish, scalelike, dry. ( Pedicels horizontal to erect (recurved); bracteoles 2, brownish, scalelike, basal.) Flowers bisexual, weakly bilaterally symmetric (radially symmetric in R. columbianum, R. groenlandicum, R. tomentosum, scented or not); sepals 5[-9], slightly connate; petals 5[-9], strongly to only slightly connate (sometimes nearly distinct), corolla deciduous, rotate to campanulate or funnelform; stamens 5-12[-20], included to long-exserted; (filaments usually unequal, usually unicellular-hairy, glabrous in R. vaseyi, glabrous or proximally unicellular-hairy in R. groenlandicum, R. lapponicum); anthers without awns, dehiscent by terminal pores; ovary 5[-18]-locular; style inserted in slight depression at ovary apex or smoothly intergrading, (usually curved, long, slender); stigma capitate. Fruits capsular, elongate, usually ovoid to cylindric, dehiscence usually basipetally septicidal (acropetally septicidal in R. columbianum, R. groenlandicum, R. tomentosum). Seeds (10-)100+, flattened-ellipsoidal to fusiform, often tailed, ± winged; testa smooth. x = 13.
Shrubs or trees, terrestrial or epiphytic, with various hairs, and/or with peltate scales or glabrous, indumentum sometimes detersile (the hairs tangled and coming away as a layer). Leaves evergreen, deciduous or semideciduous, alternate, sometimes clustered at stem apex; margin entire, very rarely crenulate, abaxial indumentum sometimes with a pellicle (a thin skinlike layer on the surface). Inflorescence a raceme or corymb, mostly terminal, sometimes lateral, few-to many-flowered, sometimes reduced to a single flower. Calyx persistent, 5–8-lobed, sometimes reduced to a rim, lobes minute and triangular to large and conspicuous. Corolla funnelform, campanulate, tubular, rotate or hypocrateriform, regular or slightly zygomorphic, 5(–8)-lobed, lobes imbricate in bud. Stamens 5–10(–27), inserted at base of corolla, usually declinate; filaments linear to filiform, glabrous or pilose towards base; anthers without appendages, opening by terminal or oblique pores. Disk usually thick, 5–10(–14)-lobed. Ovary 5(–18)-locular, with hairs and/or scales, rarely glabrous. Style straight or declinate to deflexed, persistent; stigma capitate-discoid, crenate to lobed. Capsule cylindrical, coniform, or ovoid, sometimes curved, dehiscent from top, septicidal; valves thick or thin, straight or twisted. Seeds very numerous, minute, fusiform, always winged, or both ends with appendages or thread-like tails.
Evergreen or deciduous trees, shrubs, or prostrate shrublets, sometimes epiphytic, either scaly (lepidote rhododendrons) or lacking scales (elepidote rhododendrons). Lvs alternate, entire or rarely ± serrulate, petiolate. Fls mostly in terminal panicles, racemes or umbels, much less commonly axillary or solitary, pedicellate, with deciduous scales (perulae). Calyx 5-(10)-lobed, accrescent but sometimes reduced to a rim. Corolla 5-(10)-lobed, very variable in shape but generally campanulate, funnelform or broadly tubular, usually slightly zygomorphic. Stamens usually 5-10, sometimes more, commonly twice as many as corolla lobes, included or exserted; anthers with apical pores. Fr. a woody septicidal capsule, usually ovoid to oblong. Seeds numerous, minute.
Cal 5-lobed, much shorter than the cor; cor campanulate to funnelform, conspicuous, regularly or commonly irregularly 5-lobed; stamens mostly 5 or 10, with elongate filaments and short anthers with 2 terminal pores; ovary superior, 5-locular; style elongate; capsule septicidal; shrubs or trees with alternate, deciduous or evergreen lvs and showy fls in terminal racemes or umbel-like clusters from scaly buds. Our spp. 2n=26, except as noted. (Azalea) 850, mainly N. Hemisphere.
Scales sessile, flat, slightly impressed, generally of two different sizes (i.e. very many smaller, and fewer much larger ones, irregularly mixed), all very dense, touching or partly overlapping each other, the centre very dark (sooty to blackish brown) and large in relation to the paler marginal zone, the latter irregularly several-lobed or-incised up to the centre (the broad lobes again, but more shortly lobed) and becoming silvery in later stages.
Scales +-dendroid, each on top of a distinct and ± persistent epidermal tubercle, thus both surfaces or at least the undersurface of the leaves densely tubercled and scabrid or rough to the touch in later glabrescent stages; marginal zone usually wide, deeply, often narrowly incised (then becoming similar to a stellate hair). Corolla various, mostly shortly tubular and +-zygomorphous, rarely elongate and funnel-or salver-shaped.
Scales disk-shaped, i.e. their marginal zone entire or almost so (at most slightly—regularly or mostly irregularly—crenulate) and narrow in relation to the generally darker, often thick or swollen centre, on the branchlets and/or the pedicels sometimes on top of thick, persistent, wart-like stalks. Corolla mostly ± shortly tubular, rarely funnel-shaped or (tubular-)campanulate, lobes erect to spreading.
Scales star-shaped to various degree, mostly flat, rarely subdendroid, rarely each on top of a low, hardly permanent epidermal tubercle, ± equal in size, distant from each other. Corolla tubular, salver-shaped, tube straight or slightly curved, long and narrow, lobes relatively short (at most ¼ as long as the total corolla), spreading ± horizontally.
Scales disk-shaped, entire or nearly so (subcrenate), their marginal zone narrower and thinner than the mostly thick centre. Corolla salver-shaped, tube elongate and +-narrow, straight or slightly curved, lobes equalling ¼ or less of the total length of the corolla, spreading ± horizontally.
Scales 'star-shaped' to various degree, mostly (rather) small, already distant from each other on the young leaves, the thin marginal zone ± irregularly dented or lobed, often early dissolute (the remaining centre then giving the impression of a disk-shaped scale).
Plants elepidote. Leaves persistent or deciduous in the wild state in Asia, persistent in Malesia including the cultivated species introduced from Asia. Flowers (1-3, rarely more), from the terminal bud; leafy shoots from the axil of lower perulae of the same bud.
Compact shrub, forming cushions or mats, very densely foliate. Leaves linear-lanceolate or oblanceolate. Flowers solitary, or more rarely in twos, nodding from the apex of a robust, upright pedicel which is much outstanding above the foliage.
Leaves densely tomentose or villous by simple hairs initially (new shoots) or in young stages at least beneath, mostly glabrescent at maturity, margin ± cartilaginous characteristically undulated when dry; nerves 12-20, ± parallel.
Scales very dense, in general rather large, touching or slightly overlapping each other, forming a coherent layer on the undersurface of (sub)mature leaves, which is persistent for a rather long time. Corolla of various shape.
Leaves medium-sized, (0.6-)1-4 (rarely in part in the same specimen up to 7) by (0.4-)1-2 (rarely in part in the same specimen up to 2.5, very rarely up to 3) cm, of various form other than linear or narrow-lanceolate.
Plants entirely elepidote. Leaves evergreen. Flowers from terminal buds (several to many); leafy branchlets (new foliate shoots) from separate lateral buds, from the axils of the leaves of the past season.
Plants entirely elepidote. Leaves evergreen. Flowers from terminal buds (several to many); leafy branchlets (new foliate shoots) from separate lateral buds, from the axils of the leaves of the past season.
Plants entirely elepidote. Leaves deciduous. Flowers (several to many) from a strictly floral terminal bud; leafy shoots from lateral buds below, i.e. from the axils of the leaves of the past season.
Floral buds, respectively inflorescences, though seemingly terminal, in reality lateral, mostly several together, starting from the axil(s) of the uppermost leaf (or leaves).
Plants lepidote, i.e. covered with scales (epidermal trichomes) at least on the undersurface of the young leaves, generally also on the branchlets and in the floral region.
Leaves linear or narrow-lanceolate, opposite or in 3-8 (sometimes up to 15)-merous pseudowhorls, 3-7 (rarely up to 11) mm wide (at least 1.3 cm long, mostly much longer).
Branchlets with appressed, flattened, mostly brown hairs, or with flattened and normal (not-flattened) hairs. Leaves ± scattered on the branchlets, +-strigose.
Leaves rather large, all or at least for their greater number in the same specimen longer than 4 cm, mostly much longer, and of various shape.
Leaves very small, 3-10 (rarely in part up to 20) by 2-6(-7, rarely up to 8) mm. Slender, often dwarf, terrestrial or epiphytic shrubs.
Calyx small or obscure. Stamens 10. Seeds shortly and irregularly winged at both ends.
Differs from all other series of subsect. Euvireya by having only 5 stamens.
Seeds manifestly appendaged by ± long tails or wings at both ends.
Leaves linear, 1-1.5 mm wide, in dense ± 20-merous pseudowhorls.
Stamens 5. Corolla funnel-shaped.
