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FOC | Family List | FOC Vol. 19 | Rubiaceae

37. Hymenodictyon Wallich in Roxburgh, Fl. Ind. 2: 148. 1824.

土连翘属 tu lian qiao shu

Authors: Tao Chen & Charlotte M. Taylor

Shrubs or trees [or sometimes epiphytic or lianescent], usually deciduous, unarmed; bark notably bitter. Raphides absent. Leaves opposite, usually with domatia; margins rarely irregularly lobed and/or serrate; stipules deciduous, interpetiolar, triangular to ligulate, entire or glandular-serrate, usually strongly reflexed. Inflorescence terminal and/or axillary, spiciform to racemiform or sometimes paniculate with axes racemiform or spiciform, many flowered, erect to pendulous, pedunculate, bracteate with 1-4 leaflike to petaloid, stipitate, veined basal bracts and other bracts usually reduced [or sometimes well developed]. Flowers sessile to shortly pedicellate, bisexual, monomorphic. Calyx limb deeply 5(or 6)-lobed. Corolla white, green, yellow, or red, funnelform or narrowly campanulate, inside glabrous; lobes 5, valvate in bud, apparently often ascending or remaining partially closed at anthesis. Stamens 5, inserted in corolla tube below throat, included; filaments short, flattened; anthers basifixed, sagittate at base. Ovary 2-celled, ovules several to numerous in each cell on axile placentas; stigma fusiform or capitate, well exserted. Infructescences with pedicels and sometimes peduncles often elongating and/or becoming reflexed. Fruit capsular, ellipsoid-oblong to obovoid or ellipsoid, loculicidally dehiscent into 2 valves, woody to cartilaginous, with calyx limb deciduous; seeds numerous, medium-sized, flattened, with broad, membranous, shortly erose, basally 2-lobed wing; endosperm fleshy; embryo small; cotyledon oblong or orbicular.

Twenty-two species: Africa, tropical Asia, and Madagascar; two species in China.

The flowers apparently all open nearly simultaneously on a plant, probably within a very few days at most. The corolla lobes appear to remain partly closed when the flower is mature and the stigma well exserted; Razafimandimbison and Bremer (Bot. J. Linn. Soc. 152: 335. 2006) reported that the flowers are protandrous, so this may be a secondary position after the anthers have released their pollen and while the stigma is receptive. Occasional irregularly lobed leaves, similar to those of plants of Hymenodictyon, are found in a few other Rubiaceae genera (e.g., Simira Aublet of the Neotropics).

W. C. Chen (in FRPS 71(1): 227. 1999) described the corolla lobes as imbricate in bud and the anthers as dorsifixed, but Bridson and Verdcourt (Fl. Trop. E. Africa, Rub. (Pt. 2), 452. 1988) and Razafimandimbison and Bremer (loc. cit.) described them as valvate and basifixed, respectively, which corresponds to observations of Chinese specimens (Henry 12150, MO!).

1 Inflorescences axillary, at each leaf axil simple, with 1 racemiform or spiciform axis; leaf blade glabrous to glabrescent on both surfaces or sometimes pilosulous abaxially.   1 H. flaccidum
+ Inflorescences axillary and sometimes also terminal, simple or at least part branched and paniculate with several spiciform to racemiform axes; leaf blade pilosulous on both surfaces.   2 H. orixense

Lower Taxa


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