Type: — CHINA. Guangxi Zhuangzu Autonomous Region, Jingxi City, Anning Town, in hillside of limestone area, rare, alt. 1000 m a.s.l., in flowers, 9 May 2016, D. X. Nong & Y. D. Peng 451025160509001 LY (holotype GXMG!; isotype CMMI!); the same locality, in fruits, 11 October 2014, Y. D. Peng et al. 451025141011024 LY (paratype GXMG!).

Evergreen tree, up to 18 m tall, trunk to 50 cm d. b. h., bark dark brown, irregularly scaly and flaking; young branches green, puberulous. Leaves alternate, elliptic or ovate, 8–14 × 3.5–5.5 cm, leathery, glabrous except along midrib on the lower surface, adaxially dark green and lustrous, abaxially slightly paler, brownish when dry; margin entire, slightly revolute; base rounded to obtuse, apex acute; midrib prominent on the lower surface, depressed on the upper surface; lateral veins 6–8 per side, slender, arched and anastomosing well away from the margin, inconspicuous on upper surface, prominent on lower surface; reticulate veins distinct on the lower surface; petiole 5–8 mm long, puberulous. Male flowers not seen. Female flowers solitary, axillary on current year’s branches; pedicel short, 2–3 mm long, densely brown strigose. Calyx lobes 4, divided to the middle, broadly triangular, 1 mm long, 2 mm wide, densely brown strigose outside, glabrous inside; corolla pale yellow, fragrant; corolla tube quadrangular, ca. 5 mm long, 6 mm in diam.; corolla urceolate, divided to the middle; lobes 4, reflexed, ca. 6 mm long, 3 mm wide; densely white sericeous outside and smooth inside; staminodes 8, adnate to base of corolla, glabrous, ca. 2 mm long. Ovary ovoid, ca. 4 mm long, ca. 3 mm in diam., glabrous, 8-locular; stigmas 4. Fruiting pedicel ca. 3 mm; fruiting calyx nonpersistent; berry orange-yellow when mature, globose or depressed at both ends, 6–8(–10) cm in diam., glabrous. Seeds 6–8, brown, laterally compressed, 35 × 22 × 15 mm, with longitudinal grooves on the surface. The flowers occur in April to May, fruits mature in September to October.

Etymology: —The specific epithet‘ microcalyx ’refers to the species’ small calyx lobes.

Distribution:— The species is currently known only from Jingxi city, southwest of Guangxi, China. It probably may be also found in other isolated rocky limestone mountains of northern Vietnam.

Habitat & ecology:— Diospyros microcalyx grows on karstic rocky limestone slopes, in open secondary shrubs, at ca. 1000 m in elevation, in association with e.g. Phoebe nigrifolia S. Lee & F. N. Wei (1979:58), D. siderophylla H. L. Li (1943:450), Nephrolepis cordifolia (L.) C. Presl (1836:79) and Pseudochirita guangxiensis var. glauca Y. G. Wei & Yan Liu (2004:555). This area is being destroyed by human impacts such as fuel wood cutting, grazing and small scale agriculture, making the species likely to become threatened in the future.

Conservation status:— The species should be considered Data Deficient (DD) according to IUCN Red List criteria (IUCN 2016) because it is known from only one collection and thus remains in need of further investigation with respect to future conservation efforts.

Taxonomic relationships:— In general appearance Diospyros microcalyx is very distinct from any other known species of this genus, the fruiting calyx absent when ripe. Also the small calyx lobes and the large fruits are rather rare in Diospyros. The closely related species is D. insidiosa Bakh., distributed in Malay Peninusula, Indonesia and Thailand, but it can be easily distinguished by the fruiting calyx (fruiting calyx nonpersistent in D. microcalyx vs. fruiting calyx divided to the base, flattened, lobes reflexed in D. insidiosa Bakh.).