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Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 32, Number 2
Spring 1978

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Two New Rhododendrons Species And A New Variety
H. H. Davidian, Edinburgh, Scotland

Rhododendron adenosum Davidian, sp. nov.
        Species R. glischro Balf. f. et W. W. Sm. affinis sed foliis infra esetulosis, apice acutis vel obtusis, calyce minore 4-5 mm. longo, inflorescentia 4-8flora, foliis plerumque minoribus recedens. rutex vel arbor parva ad 5 m. alta; ramuli floccosi vel glabai, dense setuloso-glandulosi, sub inflorescentia 4-6 mm. diametro, perulis deciduis. Folia sempervirentia; lamina coriacea, ovato-lanceolata vel lanceolata, 7-12.8 cm. longa, 2-5 cm. lata, apice acuta vel obtusa et mucronata, basi rotundata vel leviter cordata, supra atroviridis vel oliacea, levia, plana, opaca, moderate vel sparsim floccosa vel glabra, esetulosa, setuloso-glandulosa vel eglandulosa, costa media sulcata, floccosa vel glabra, moderate vel sparsim setuloso-glandulosa vel eglandulosa, venis primariis 12-16 impressis; margine plano esetuloso, setuloso-glanduloso vel eglanduloso; infra pallide viridis, glabra vel dense tomentosa, esetulosa, dense vel moderate glandulosa, costa media prominente, tomentosa vel glabra, esetulosa, dense vel moderate setuloso-glandulosa, venis primariis elevatis; petiolus 0.8-2.3 cm. longus, supra sulcatus, floccosus vel glaber. Inflorescentia racemoso-umbellata 4-8flora, bracteis deciduis; rhachis 0.61.2 cm. longa, pubescentia, eglandulosa; pedicelli 1.5-3 cm. longi, tomentosi, esetulosi, dense setuloso-gland ulosi. Calyx 5-lobatus, 4-5 mm. longus, pallide viridis, lobis lanceolatis vel ovatis, extra tomentosis vel glabris, dense vel moderate glandulosis, margine glabris, glandulosis. Corolla campanulata, 3-5.3 cm. longa, alba roseo-tincta vel alba basi atro-rubro-notata vel nota carente, atro-rubro-maculata vel immaculata; lobi 5, 1-2.4 cm. longi, 1.4-3 cm. lati, rotundati emarginati. Stamina 10 vel raro 13 inaequalia, 1.8-4.6 cm. longa; filamenta basi puberula. Gynoecium 3.2-5 cm. longum; ovarium conoideum, 3-4 mm. longum, glabrum vel raro pubescens, glandulis longe pedicellatis ascendentibus dense praeditum, 5-6-loculare; stylus glaber eglandulosus. Capsula gracilis vel oblonga, 1.6-2.1 cm. longa, 3-5 mm. lata, paulo curvata vel recta, tomentosa vel glabra, moderate vel dense setulosoglandulosa, calyce persistente.

        S. W. Szechuan. Mountains of Kulu. Alt. 3380 m. Shrub, 3-5 m. In spruce forests. July 1929. J. F. Rock No. 18040.
        S. W. Szechuan. Mountains of Kulu. Alt. 3540 m. Shrub or tree, 3-4 m. In hemlock forest. Sept. 1929. J. F. Rock No. 18226.
        S. W. Szechuan. Mountains of Kulu. Alt. 3540 m. Shrub, 2-2.5 m. In spruce forest. Sept. 1929. J. F. Rock No. 18228 (Holotype in Herb. Hort. Bot. Edin. Details of the flower are taken from a cultivated plant).

        This plant has been known under the name R. glischrum var. adenosum. It is so distinct in cultivation, that it merits specific rank.
        R. adenosum was discovered by Rock in July 1929 on the mountains of Kulu, south-west Szechuan. It was again found by him later in September in the same region. The plant grows in spruce and in hemlock forests, at elevations of 11,081-11,606 feet.
        The species belongs to the Glischrum Subseries, Barbatum Series. It bears a resemblance to R. glischrum in some features, but is readily distinguished by the very short hairs and glands on the lower surface of the leaves, by the short calyx, and usually by the fewer-flowered inflorescence and shorter leaves.
        It was introduced by Rock in 1929. Two colour forms are in cultivation, white, and white flushed pink. The plant is hardy and very free-flowering in April or May. It is uncommon in cultivation, but is well worth a place in every collection of rhododendrons.

        A shrub or small tree 2-5 m. high; branchlets hairy or glabrous, rather densely setulose-glandular, those below the inflorescences 4-6 mm. in diameter, leaf-bud scales deciduous. Leaves evergreen, ovate-lanceolate or lanceolate, lamina coriaceous, 7-12.8 cm. long, 2-5 cm. broad, apex acute or obtuse, base rounded or cordulate; upper surface dark green or olive green, not rugulose, flat, mat, moderately or sparsely hairy or glabrous, not setulose, setulose-glandular or not setulose-glandular, midrib grooved, hairy or glabrous, moderately or sparsely setulose-glandular or not setulose-glandular, primary veins 12-16 on each side, deeply impressed; margin flat, not setulose, setulose-glandular or not setulose-glandular; under surface pale green, not hairy or rather densely hairy with very short hairs, discontinuous, not setulose, rather densely or moderately glandular with long - or medium-stalked glands, discontinuous, midrib prominent, not hairy or hairy, not setulose, rather densely or moderately setulose-glandular in its entire length or in the lower half, primary veins raised; petiole 0.8-2.3 cm. long, grooved above, not hairy or hairy, not setulose, rather densely or moderately setulose-glandular. Inflorescence a lax recemose umbel of 4-8 flowers, flower-bud scales deciduous; rhachis 0.6-1.2 cm. long, pubescent, not setulose-glandular; pedicel 1.5-3 cm. long, hairy with small hairs, not setulose, rather densely setulose-glandular. Calyx 5-lobed, 4-5 mm. long, pale green, lobes lanceolate or ovate, outside hairy with short hairs or not hairy, rather densely or moderately glandular with medium - or long stalked glands, margin glabrous, glandular with medium - or long stalked glands. Corolla campanulate, 3-5.3 cm. long, white tinged pink or white, with or without a crimson blotch at the base, and with or without crimson spots; lobes 5, 1-2.4 cm. long, 1.4-3 cm. broad, rounded, emarginate. Stamens 10 or rarely 13, unequal, 1.8-4.6 cm. long; filaments puberulous at the base. Gynoecium 3.2-5 cm. long; ovary conoid, 3-4 mm. long, glabrous or rarely hairy with long hairs, densely glandular with long-stalked ascending glands, 5-6-celled; style glabrous, eglandular. Capsule slender or oblong, 1.6-2.1 cm. long, 3-5 mm. broad, slightly curved or straight, hairy orglabrous, moderately or rather dense-ly setulose-glandular, calyx lobes persistent.

Rhododendron luteiflorum Davidian, sp. nov.
        Species R. glaucophyllo Rehder affinis sed floribus viridulo-flavidis, foliis infra squamis laxioribus inter se 3-8 diametris distantibus praedita, et aream allopatricam habitans differt.
        Frutex patens vel rectus 75 cm. - 1.50 m. altus, cortice levi brunneo desquamante, ramulis lepidotis. Folia sempervirentia; lamina coriacea, aromatics, lanceolata, oblanceolata vel oblongo-lanceolata, 4-6.8 cm. longs, 1.5-2.6 cm. lata, apice rotundata vel obtusa et mucronata, basi cuneata, obtusa vel rotundata, paulo decurrens vel haud decurrens; supra atroviridis nitens elepidota vel lepidota; infra conspicue glauca, squamis minoribus pallide flavidis inter se 3-8 diametris distantibus, squamis majoribus atrobrunneis dispersis; petiolus 0.71.2 cm. longus, lamina decurrente anguste alata, vel rotundatus, moderate vel dense lepidotus. Inflorescentia terminalis, umbellata vel breviter racemose, 3-6-flora, bracteis deciduis; rhachis 3-5 mm. longs, lepidota; pedicelli 0.8-1.5 cm. longi, corollae breviores, dense vel moderate lepidoti. Calyx globatus magnus 6-8 mm. longus, lobis lanceolatis vel ovato-lanceolatis, apice acutis, extra lepidotis, margine eciliatis. Corolla campanulata, 2-2.2 cm. longa, 5-lobo, viridulo-flavida, immaculata, extra lepidota vel elepidota. Stamina 10 inaequalia, 1-1.5 cm. longa, corollae breviora; filamenta basi vel in trientibus decobus inferioribus dense pubescentia. Ovarium conoideum vel oblongum, 5 mm. longum, 5-loculare, dense lepidotum; stylus longus validus curvatus, corollae brevior, elepidotus. Capsula conoidea vel oblongo-ovalis, 5-7 mm. longa, 5-6 mm. lata, dense lepidota, calycis lobis persistentibus circumcinctis.

        North Burma. North Triangle. Uring Bum, above Akkail. 9500 feet. Rhododendron sp. affin. R. glaucophyllum. A small more or less erect shrub or undershrub, growing in dense bushy thickets on the open granite ridge with several other species of Rhododendron and Vaccinium, Gaultheria, etc. Probably dwarfed in the open - here about 3 feet tall. Flowers over. This is probably its lower limit. F. Kingdon-Ward, No. 20845.
        North Burma. North Triangle, Tama Bum. 10,000-11,000 feet. June 20, 1953. Rhododendron pruniflorum? A bushy shrub, 3-5 feet tall. Leaves glaucous and scaly beneath. Style glabrous. Flowers not seen, three per truss. Bark flaky. Fruiting; not common in thickets along the ridge. (Same as No. 20845?). F. Kingdon-Ward, No. 21041.
        North Burma. North Triangle. Uring Bum, above Akkail, 10,000 feet. November 4, 1953. Rhododendron sp. Series Glaucophyllum. A dwarf scrub plant growing socially on the exposed crest of the ridge. In more sheltered spots opening its buds. Flowers lemon yellow. (So this is neither R. pruniflorum nor R. glaucophyllum. The colour is much better than that of R. hypolepidotum.) Anthers red-brown, base of filament puberulous. Style glabrous. Same as No. 20845, and probably No. 21040. F. Kingdon-Ward, No. 21556 (Holotype in Herb. Brit. Mus. Nat. Hist.).

        This plant was at first described as R. glaucophyllum var. luteiflorum. Further investigation of specimens and plants in cultivation shows that it merits specific status.
        Kingdon-Ward discovered this plant in June 1953 at Tama Bum, North Triangle, North Burma. He collected it again later in November at Uring Bum, above Akkail in the same region. It grows in dense bushy thickets on open granite ridges, at elevations of 9,500 - 11,000 feet.
        The species is a member of the Glaucophyllum Subseries, Glaucophyllum Series. It is allied to R. glaucophyllum from which it differs markedly in its lemon-yellow or greenish-yellow flowers, in the scaly lower surface of the leaves, the scales being 3-8 times their own diameter apart, usually in the larger leaves, and often in the somewhat different habit of growth. It also differs in its geographical distribution. R. luteiflorum comes from North Burma, whereas R. glaucophyllum is known from Nepal, Sikkim, Bhutan and Assam.
        The plant was introduced by Kingdon-Ward under No. 21040, in 1953. It is one of the finest yellow-flowered dwarf rhododendrons in cultivation. Other remarkable features of this plant are the markedly glaucous lower surface of the leaves, the large leafy lanceolate or ovate-lanceolate calyx, and the smooth, brown, flaking bark of the stem and branchlets. It is hardy, but to be able to grow it satisfactorily along the east coast and in gardens inland, a well-sheltered position should be provided. The species was given the Award of Merit in 1960 and the First Class Certificate in 1966 when exhibited by the National Trust for Scotland, Brodick Castle Gardens.

        A rounded spreading or broadly upright shrub, 75 cm. - 1.50 m. high; stem and branchlets with smooth, brown, flaking bark; branchlets scaly. Leaves evergreen, lanceolate, oblanceolate or oblong-lanceolate, aromatic, lamina coriaceous, 4-6.8 cm. long, 1.5-2.6 cm. broad, apex rounded or obtuse, mucronate, base tapered, obtuse or rounded, slightly decurrent on the petiole or not decurrent; upper surface dark green, shining, not scaly or scaly; under surface markedly glaucous, laxly scaly, the smaller pale yellow scales 3-8 times their own diameter apart, the larger dark brown scales widely separated; petiole 0.7-1.2 cm. long, margins slightly winged or ridged or rounded, moderately or rather densely scaly. Inflorescence terminal, umbellate or shortly racemose, 3-6-flowered, flower-bud scales deciduous; rhachis 3-5 mm. long, scaly; pedicel 0.8-1.5 cm. long, shorter than the corolla, rather densely or moderately scaly. Calyx large, leafy, 5-lobed, 6-8 mm. long, lobes lanceolate or ovate-lanceolate, apex acute, outside scaly, margin not ciliate. Corolla campanulate, 2-2.2 cm. long, 5-lobed, lemon-yellow or greenish-yellow, without spots, outside scaly or not scaly. Stamens 10, unequal, 1-1 .5 cm. long, shorter than the corolla; filaments densely pubescent at the base or in the lower two-thirds of their length. Ovary conoid or oblong, 5 mm. long, 5-celled, densely scaly; style somewhat long, stout, sharply bent, shorter than the corolla, not scaly. Capsule conoid or oblong-oval, 5-7 mm. long, 5-6 mm. broad, rather densely scaly, enclosed by the persistent calyx lobes.

Rhododendron zaleucum Balf. f. et W. W. Sm. var. flaviflorum Davidian, var. nov.

        Aspectu R. zaleuci Balf. f. et W. W. Sm. sed flonbus flavis, foliis majoribus ad 10 cm. longis recedens.

        North Burma. North Triangle (Uring Bum, above Akkail) 9000 feet, 14 May 1953. Probably a new species. Rhododendron sp. ยง Triflorum. A small tree up to about 25 feet high. Like R. triflorum in some respects, but flowers much larger, trusses more crowded, corolla a purer yellow. Actually the flowers vary in colour, white, yellow, almost salmon. A beautiful species now in full bloom. Common along the exposed ridge. F. Kingdon-Ward No. 20837 (Holotype in Herb. Brit. Mus. Nat. Hist.)

        The variety differs from the species in its yellow flowers, and in the larger leaves, lamina up to 10 cm. long.
        Kingdon-Ward discovered this plant in May 1953 at Uring Bum, above Akkail, North Triangle, North Burma, at an elevation of 9,000 feet. He records it as being common along the exposed ridge. The plant was introduced by him the same year (K. W. No. 20837).
        In its native home the variety is a small tree up to 25 feet high, although in cultivation it is a broadly upright shrub up to 6 feet in height, fairly well filled with foliage. It is a vigorous grower, and is of great beauty when covered with large funnel-shaped yellow flowers. The plant is hardy in a sheltered position, and is worthy of being grown in every collection of rhododendrons.

Rhododendron montroseanum Davidian H. H. Davidian, Edinburgh, Scotland

        Rhododendron mollyanum from south-east Tibet, described in 1954, must have a new name, because at an earlier date in 1909, the name R. mollianum (sic) had been given to a rhododendron from New Guinea. The Tibetan plant will now be named R. montroseanum, in honor of the late Duchess of Montrose. The change in nomenclature may be regretted, but is strictly in accordance with the International Code Of Botanical Nomenclature. (It may be remarked that R. mollyanum was also named after the same Duchess of Montrose who was known to her family as "Molly").


Volume 32, Number 2
Spring 1978

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