Ridsdalea J.T.Pereira & K.M.Wong (in Wong and Pereira 2016: 42).

Van Phung, Khoa, Averyanov, Leonid V., Maisak, Tatiana V., Krupkina, Ludmila I., Cao, Hai Xuan & Nguyen, Cuong Huu, 2024, Checklist of the genus Ridsdalea (Rubiaceae, Gardenieae) in Vietnam with description of the new species R. backanensis, PhytoKeys 239, pp. 1-12 : 1

Ridsdalea J.T.Pereira & K.M.Wong (in Wong and Pereira 2016: 42).

Type.

Ridsdalea grandis (Korth.) J.T.Pereira (in Wong and Pereira 2016: 46). ≡ Gardenia grandis Korth. ( Korthals 1851: 191).

Description.

Large shrubs to small, medium or large trees with unarmed trunk and branches. Branches opposite and decussate on the trunk, sympodial in development. Leaves opposite or verticillate in groups of 2-3, each trifoliate group based on a distal node with only one leaf normally developed and the proximal node with a pair of normal leaves; leaves petiolate to subsessile, axils of the midrib, secondary veins, and sometimes other vein junctions frequently with domatia on the abaxial leaf surface; margin entire. Stipules interpetiolar, without distinct venation, free or hardly fused at the base, persistent to caducous, inner surface hairy with colleters restricted to 1-several rows. Inflorescence terminal or pseudoaxillary (terminal in origin, later appearing lateral because of displacement to one side during sympodial branch development), distinctly cymose, several-flowered or sometimes reduced to a 1-flowered structure, distinctly pedunculate to subsessile. Flowers bisexual, pedicellate or sometimes subsessile, small or large with corolla tube less than 15 cm long. Calyx 5-8(-10)-lobed, colleters present in small groups on the inner surface, glabrous or glabrescent to hairy on the outside. Corolla commonly 5-, rarely 6-8-merous; hypocrateriform or campanulate; the tube white or white with reddish purple speckles or blotches inside, the outer and inner surface glabrous or hairy; lobes contorted to the left in the flower bud; stamens attached at the upper part of the corolla tube, anthers sessile or subsessile, linear or narrowly lanceolate; style shorter than, as long as, or slightly exceeding the corolla tube, mostly glabrous; stigma clavate to fusiform, 2-lobed, smooth to somewhat ribbed; ovary 2-celled; ovules many; placentation axile. Mature fruits baccate, indehiscent, globose or broadly ellipsoid, 2-5 cm across, 2-locular, outer surface smooth. Seeds many, immersed in a dark brown pulp-like placental tissue ( Chen and Taylor 2011; Wong and Pereira 2016).

32 species in Myanmar, SW China, Thailand, Laos, Cambodia, Vietnam, Malacca Peninsula. Indonesia, Philippines, New Guinea. In Vietnam 6 species (2 endemic, found in Bac Kan and Lam Dong provinces).