﻿Xantolisweimingii (Sapotaceae), a new species from the Yuanjiang River basin, Yunnan, southwest China

﻿Abstract Xantolisweimingiisp. nov. (Sapotaceae) is described and illustrated from Yunnan, southwest China. The new species is morphologically most similar to X.tomentosa (Roxb.) Raf., but differs from the latter in the ovate or obovate leaves, entirely glabrous corollas, lanceolate, ca. 5 mm long staminodes, fringed at the base. We provided a distribution map and a preliminary conservation assessment for the new species. Additionally, an updated dichotomous key to all known species of Xantolis is presented.


Introduction
Xantolis Raf.(Sapotaceae, Chrysophylloideae) is a small genus of trees and shrubs that comprises approximately 14 species (van Royen 1957;Swenson and Anderberg 2005).Its distribution ranges from the eastern Himalayas to the Philippines in tropical Asia (van Royen 1957;Li 1987;Li and Pennington 1996).This genus is morphologically characterized by having obvious spines, acute anther appendages, lanceolate lobes of calyx and corolla, and aristate staminodes (Swenson and Anderberg 2005).Some members of the genus are of significant economic importance due to their edible fruits and high-quality timber (Li 1987).
The systematic position of Xantolis has been controversial.Pennington (1991) classified it as a member of the large tribe Chrysophylleae.Recent studies based on molecular data have demonstrated that Xantolis is recovered as a sister to the rest of the subfamily Chrysophylloideae, being a very isolated and poorly understood genus (Anderberg and Swenson 2003;Bartish et al. 2005Bartish et al. , 2011;;Swenson and Anderberg 2005).Therefore, further extensive sampling is still required to test the monophyly and synapomorphic characters, generic status, and phylogenetic position of Xantolis (Triono et al. 2007;Stride et al. 2014;Swenson et al. 2023).
The Yuanjiang River is the mainstream of the upper reaches of the Hong (Red) River, while the Luzhijiang River, situated in central Yunnan in southwest China, is an upper tributary of the Hong River.The rain shadow effect created by the Ailao-Wuliang Mountains and the Yunnan-Guizhou Plateau results in a distinctive hot and dry climate in these valleys, in contrast to most of the surrounding regions (Jin and Ou 2000;Li et al. 2016).The climate in this region is characterized by a dry season (which can be further divided into a cool dry season from November to February and a hot dry season from March to April), with an annual average temperature of 24 °C and a mean annual evaporation capacity of 2700-3800 mm, which is three to six times higher than the mean annual precipitation (600-800 mm).There is also a wet season from May to October, during which 80-90% of the precipitation is concentrated (Jin 2002;Shen et al. 2010;Zhou et al. 2017).The relatively closed environment of the area has led to the formation and retention of a large number of rare and endangered plants and endemic species (Li et al. 2008;Ma 2016).Knowledge of biodiversity in the region seems far from complete, with many new species being described in recent years in different lineages of organisms (Bai et al. 2015;Zhou et al. 2017;Qiao et al. 2018;Yang et al. 2019;Ding et al. 2020;Liu et al. 2022;Ma et al. 2022;Wang et al. 2022;Yang et al. 2022aYang et al. , 2022bYang et al. , 2022c;;Ma et al. 2023).
The new species of Xantolis described here, X. weimingii Huan C. Wang & Feng Yang, was first collected in the Luzhijiang Valley in August 2015.During our subsequent fieldwork, we encountered this species several times.However, only sterile or fruiting specimens were collected.In April 2022, the specimen with flowers was finally gathered in Wadie, Yuanjiang County.After a detailed comparison with morphologically similar species, we confirmed its novelty to science and describe it here as Xantolis weimingii Huan C. Wang & Feng Yang.

Materials and methods
Based on the morphological species concept defined by Cronquist (1978), the morphological studies of the new species were conducted on living plants and specimens coming from the four localities corresponding to the holotype and paratypes.The digital specimen images of similar species available at JSTOR Global Plants (https://plants.jstor.org/), the Smithsonian National Museum of Natural History (https://collections.nmnh.si.edu/search/botany/), and the Global Biodiversity Information Facility (https://www.gbif.org/)were extensively reviewed.Pertinent taxonomic literature (e.g.Clarke 1882; van Royen 1957;Aubréville 1963;Luo 1974;Wu 1977;Li 1987;Luo 1991;Li and Pennington 1996;Pham 1999;Santisuk et al. 2014;Sankara et al. 2019;Turner 2021) were extensively consulted.Measurements were taken using a ruler and a metric vernier caliper under a stereomicroscope (Olympus SZX2, Tokyo, Japan).The dot-distribution map was compiled from all specimens studied and generated with ArcGIS version 10.4 (ESRI, Inc., Redlands, USA).The conservation status was assessed using GeoCAT (online tool available at https://geocat.iucnredlist.org/) (Bachman et al. 2011) to estimate the extent of occurrence (EOO) and the area of occupancy (AOO) of the species, followed by applying the IUCN Red List Categories and Criteria (IUCN 2022) for conservation status assessment.The characters used in the identification key for the congeners mainly followed those of Van Royen (1957) and Li and Pennington (1996).Diagnosis.Xantolis weimingii is most similar to X. tomentosa (Roxb.)Raf., but can be easily distinguished by its ovate or obovate (vs.elliptic or elliptic-oblong in X. tomentosa) leaves, base broadly cuneate or nearly round (vs.cuneate), apex acute or acuminate (vs.obtuse, short obtusely or acutely acuminate), corollas entirely glabrous (vs.densely hairy at throat), 7.7-9.7 (vs.4-8) mm long, lanceolate staminodes, ca. 5 (vs.3-3.5) mm long, apex acuminate into an awn, fringed at the base (vs.broad base, not fringed), glabrous (vs.hairy).
Preliminary conservation assessment.Xantolis weimingii is at a restricted geographic range, with an estimated extent of occurrence (EOO) of 139.594 km 2 and an area of occupancy (AOO) of 12 km 2 .Four populations of the new species have been discovered: two of them from the same locality (Yimen County), and one in the Yuanjiang National Nature Reserve.Unfortunately, these populations are typically small, ranging from three to a maximum of eight plants.So far, we have not found any saplings or seedlings in the Yuanjiang and Fawu populations, and we judged that the self-renewal capacity of the wild population of this species is low.The other populations in the Luzhijiang River valley at Yimen County are most threatened.The hillside land here is highly degraded and soil erosion is serious due to mining operations.Furthermore, residents had been harvesting the plant for firewood, resulting in the plant becoming a shrub-like appearance.Therefore, Xantolis weimingii is at a high risk of extinction due to Discussion.Xantolis weimingii can be easily distinguished from its congeners by the following combination of characters: plants densely covered with ferruginous arachnoid-lanate, leaves ovate or obovate, and staminodes fringed at the base.It is most similar to X. tomentosa (excluding the synonym Planchonella dongnaiensis Pierre ex Dubard), which is widely distributed in Sri Lanka, India, and Myanmar.However, it differs clearly from the latter by having pale gray (vs.light reddish brown in X. tomentosa) barks, ovate or obovate (vs.elliptic, elliptic-oblong) leaves, 2-8 (vs.4-14) cm long, 1.5-5.0(vs.2-6) cm wide, base broadly cuneate or nearly round (vs.cuneate), apex acute or acuminate (vs.obtuse or short obtusely or acutely acuminate), 6-9 (vs.8-l6) pairs lateral veins, 4-8 (vs.3-20) mm long petioles, 3-4 (vs. 4-7) mm long pedicels, entirely glabrous (vs.throat densely hairy) corollas, 7.7-9.7 (vs.4-8) mm long, lanceolate (vs.lanceolate-oblong or ovate) lobes, staminodes ca. 5 (vs.3-3.5) mm long, 1-2 mm wide at the base, apex acuminate into an awn, fringed at the base (vs.broad base, not fringed), glabrous (vs.hairy).Xantolis weimingii is also morphologically similar to X. cambodiana (Pierre ex Dubard) P. Royen from Indo-China.Nevertheless, X. weimingii differs from X. cambodiana in having ovate to obovate (vs.rhomboid-obovate or elliptic, sometimes lanceolate in X. cambodiana) leaves, base broadly cuneate or nearly round (vs.tapering towards the base), apex acute to acuminate (vs.obtuse, entire or retuse, sometimes short obtusely acuminate), ovate to triangular (vs.ovate or oblong) sepals, 6-7 (vs.2.5-4) mm long, 3.5-4.5 (vs.1-2) mm wide, lanceolate (vs.lanceolate or linear) staminodes, ca. 5 (vs.2-3) mm long, 1-2 (vs.ca.0.5) mm wide at the base.Xantolis weimingii shares similar fruits with X. assamica (C.B.Clarke) P. Royen, a species occurring in Assam to Bangladesh, but differs from the latter in its 4-8 (vs.5-15) mm long petioles, ovate to obovate (vs.ovate, elliptic or broadly lanceolate) leaves, 2.0-8.5 (vs.6-16.5)cm long, 1.5-5.0(vs.2-7) cm wide.

Phenology.
Flowering from April to May, and fruiting from May to October.Etymology.The new species is named after 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 China's flora of Lycophytes and Ferns and to the Herbarium of Yunnan University (Kunming, China).

Figure 1 .
Figure 1.Xantolis weimingii sp.nov.(drawn by Qiu-Ping Wang) A habit B abaxial surface of leaf C adaxial surface of leaf D flower in blooming E anthers F pistil G corolla dissected to show stamens and staminodes H calyx lobes (the upper line is the inner view, the lower line is the outer view) I fruits J side view of seed to show scar K front view of seed.

Figure 2 .
Figure 2. Xantolis weimingii sp.nov.A habit B trunk showing bark texture C branchlet D abaxial surface of tender leaf E adaxial surface of leaf F abaxial surface of leaf.

Figure 3 .
Figure 3. Xantolis weimingii sp.nov.A flowering branch B adaxial view of sepals C abaxial view of sepals D corolla dissected to show five stamens and five staminodes E corolla dissected to show five lobes F pistils G-H fruits I front view of seed J side view of seed to show scar.

Figure 6 .
Figure 6.Habitat of Xantolis weimingii A habitat of the Yuanjiang population B habitat of the Yimen population C habitat of the Eshan population.