Prof. Weiming Zhu ironwood (Xantolis weimingii) described with completely glabrous flower crowns

NEWS - Xantolis weimingii (Sapotaceae, Chrysophylloideae) is described from Yunnan, southwest China and can be easily distinguished from its relatives by the combination of densely covered plants with ferruginous arachnoid-lanate, oblong or obovate leaves and pendulous staminodes at the base.

Xantolis Raf. 1838 (Sapotaceae, Chrysophylloideae) is a small genus of trees and shrubs containing about 14 species with a distribution from the eastern Himalayas to the Philippines in tropical Asia. The genus is morphologically characterized by distinct spines, a sharp anther appendage, lanceolate lobes on the calyx and corolla, and aristate staminodes.

Molecular data suggest that the genus is sister to the entire subfamily Chrysophylloideae and is a very isolated and poorly understood genus. Specimens was first collected in the Luzhijiang Valley in August 2015, but only sterile or fruiting specimens were collected. In April 2022, a specimen with flowers was finally collected in Wadie, Yuanjiang.

The new species is most similar to X. tomentosa (Roxb.) Raf. but can be distinguished by its oblong or obverse oblong leaves, wide stony or nearly rounded base, acuminate apex, corolla entirely glabrous, 7.7-9.7 mm long, staminodes lanceolate, about 5 mm long, apex tapering to thorny, fringed at the base and glabrous.

The new species is also similar to X. cambodiana (Pierre ex Dubard) P. Royen from Indo-China, but differs by its oblong leaves, wide wedge-pointed or nearly rounded base, acuminate to acuminate apex, calyx oblong to triangular, 6-7 mm long, 3.5-4.5 mm wide, staminodes lanceolate, about 5 mm long, 1-2 mm wide at the base.

Researchers from Yunnan University, the Chinese Academy of Sciences, the Yuxi Forestry and Grassland Bureau and the Yunnan Yuanjiang National Nature Reserve Management Bureau also described X. weimingii has fruits similar to X. assamica (C.B. Clarke) P. Royen, but differs in petioles 4-8 mm long, leaves ovate to obovate, 2.0-8.5 cm long and 1.5-5.0 cm wide.

The new species was given the etymology for Professor Weiming Zhu (朱维明-Wei Ming Chu, 1930-2023), a renowned botanist from Yunnan University, in recognition of his outstanding contributions to the study of the Lycophyte flora, Chinese Ferns and to the Herbarium of Yunnan University.

X. weimingii is endemic to central Yunnan, southwest China, and is rarely collected. It has been found in four different locations to date, all in the dry and hot valleys of the Yuanjiang River and its main tributary the Luzhijiang River. The new species grows in savanna habitats on mountain slopes at elevations of 1100-1400 meters.

The rain shadow effect created by the Ailao-Wuliang Mountains and the Yunnan-Guizhou Plateau results in a typical hot and dry climate in the valleys. The climate is characterized by a dry season with an average annual temperature of 24C and an average annual evaporation capacity of 2700-3800 mm or three to six times higher than the average annual rainfall of 600-800 mm.

The new species is at high risk of extinction due to its limited geographic range, fragmented distribution, small population size and fragile environment. The researchers propose the Critically Endangered (CR) category based on the IUCN Red List Categories and Criteria (IUCN 2022).

Original research

Yang F, Chen C, Wang Q-P, Wu J-Y, Li Z-X, Wang H-C (2024). Xantolis weimingii (Sapotaceae), a new species from the Yuanjiang River basin, Yunnan, southwest China. PhytoKeys 246: 251-263, DOI:10.3897/phytokeys.246.119516