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| Ridsdalea backanensis C.H.Nguyen & Aver., in Phung, Averyanov, Maisak, Krupkina, Cao et Nguyen. 2024. |
Abstract
The paper provides an identification key and an annotated list of all six species of the genus Ridsdalea J.T.Pereira & K.M.Wong (Rubiaceae, Gardenieae) recorded in the flora of Vietnam, along with data on their valid names, synonyms, types, and distribution. A new species, R. backanensis, discovered in the limestone area of Bac Kan Province (northern Vietnam), is described and illustrated. Detailed data on its characters, ecology, distribution, phenology, preliminary IUCN conservation status, and taxonomical notes are given. The newly discovered species is potentially interesting for cultivation as an ornamental tree that may be effectively used in garden and urban green architecture.
Key words: Ba Be National Park, Bac Kan Province, endemism, flora of Vietnam, new species, plant diversity, plant taxonomy, Rothmannia
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| Ridsdalea backanensis A mature tree in natural habitat B part of crown with two main trunks C trunk of mature tree D bark at DBH E flowering and fruiting branches F, G ripe fruits H ripe fruits, sagittal section I ripe fruit, cross section J fruit, sagittal section, seeds removed K ripe seeds. Photos by C.H. Nguyen (A–E) and L. Averyanov (F–K) from plant used for preparation of the paratype voucher specimens (AL 1680), photo-correction, and design by L. Averyanov and T. Maisak. |
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| Ridsdalea backanensis A part of crown of flowering tree in natural habitat B leaves, adaxial and abaxial surface C flowering branches D flower bud and opening flower, side view E Opening flower, frontal view F, G flowers, frontal view H flowering branch showing leaves from abaxial side I flowering branch showing leaves from adaxial side J corolla, sagittal section outside and inside K peduncle, pedicels and calyxes, side view L peduncle and pedicel, side view M peduncle, pedicel, calyx and base of style, side view, corolla removed N calyx, frontal view, corolla removed O separated, upper part of calyx tube, calyx lobes, and nectary disc, frontal view P indumentum of abaxial surface of calyx on dry specimen Q portion of adaxial surface of corolla, sessile stamen and apical part of stigma R stamen S pedicel, calyx and pistil with magnified stigma, side view T apical part of stigma U middle part of stigma Photos by L. Averyanov (A, C, F–K, P) and C.H. Nguyen (B, D, E, L–O, Q–U) from plant used for preparation of the type voucher specimens (AL 1682), photo-correction and design by L. Averyanov and T. Maisak. |
Ridsdalea backanensis C.H.Nguyen & Aver., sp. nov.
Diagnosis: Ridsdalea backanensis differs from R. daweishanensis mainly in the smaller leaves, 7–11 cm long (vs. leaves 10–14 cm long in R. daweishanensis), the 1–3-flowered inflorescence (vs. inflorescences uniflorous), the much shorter pedicels, 3.5–7 mm long (vs. pedicels 20–25 mm long), the shorter subulate calyx lobes, 6.5–11 mm long (vs. calyx lobes narrowly oblanceolate, 14–16 mm long), the corolla outside sparsely hairy (vs. corolla outside glabrous), and the oblanceolate anthers, 2–3 mm wide (vs. anthers linear, about 1.5 mm wide).
Etymology: The species is named after the area of origin (Bac Kan Province, northeastern Vietnam).
Khoa Van Phung, Leonid V. Averyanov, Tatiana V. Maisak, Ludmila I. Krupkina, Hai Xuan Cao and Cuong Huu Nguyen. 2024. Checklist of the Genus Ridsdalea (Rubiaceae, Gardenieae) in Vietnam with Description of the New Species R. backanensis. PhytoKeys. 239: 1-12. DOI: 10.3897/phytokeys.239.113017
