Botanists surveying the limestone peaks of Guangxi Zhuang Autonomous Region in southern China have described a previously unknown species of the spindle-tree genus Euonymus, naming it Euonymus saxatilis in reference to its rocky karst home. The evergreen shrub or small tree, which grows one to six meters tall, was found during a field survey in July 2025 in Mulun National Nature Reserve, in the northwest of Huanjiang Maonan Autonomous County.
The genus Euonymus, a member of the family Celastraceae, comprises approximately 220 species worldwide. It originated in Europe, and most of its species are distributed in tropical and temperate regions of the Northern Hemisphere, with only a few radiating into the cold temperate zone. The diversity of the genus is concentrated mainly in southwestern China, South Asia, and adjacent Himalayan countries, and more than half of all species occur in China. Members of the genus are shrubs or small trees characterized by opposite or sub-opposite leaves, axillary thyrses, four- to five-merous flowers, stamens inserted on the disc periphery, loculicidally dehiscent capsules, and seeds enclosed by an aril.
The new species was encountered at an elevation of approximately 750 meters, where several individuals of the genus were spotted growing on the upper-middle slopes of karst mountains. The specimens showed morphological characters that clearly separated them from all previously described Euonymus species. After detailed comparisons with closely related taxa, the research team verified that the entity differs from all other congeneric species in multiple diagnostic characters, and confirmed that the morphologically closest species was Euonymus dielsianus, against which a thorough comparison with the type specimen was conducted.
That comparison focused on key diagnostic traits including leaf shape, leaf margin, inflorescence architecture, pedicel length, flower diameter, style morphology, and stamen characteristics. Euonymus saxatilis has thickly coriaceous, obovate or obcordate leaves measuring 5 to 12 centimeters long and 1.5 to 6 centimeters wide, with a margin that is sparsely and shallowly crenulate-serrulate over more than two-thirds of its length and entire for the remainder. Its cymes bear one to three flowers on peduncles 2 to 4.5 centimeters long, and the flowers, roughly 1.5 centimeters in diameter, are greenish yellow with suborbicular petals. By contrast, E. dielsianus has obovate or elliptic-obovate leaves 9 to 15 centimeters long, inflorescences of one to seven flowers, a peduncle of about 1.5 centimeters, flowers only about 0.6 centimeters across, and no style.
Several of these contrasts are particularly striking. The new species possesses a distinct style about 1.5 millimeters long and distinct filaments of roughly the same length, whereas E. dielsianus lacks a style altogether and has very short filaments. The capsules of E. saxatilis are four-lobed to the base, with ovoid lobes about one centimeter in diameter, of which one to three lobes are fertile and each carries a single mature seed. The seeds are ellipsoid, about five millimeters long, red or orange-red, and the aril is helmet-shaped, enclosing the upper half of the seed. Flowering occurs from June to July, and fruiting from September to November.
To test whether the distinctive morphology corresponds to an evolutionary lineage, the researchers generated new nuclear ribosomal internal transcribed spacer (ITS) and chloroplast trnL-F intergenic spacer sequences for the new species and combined them with published sequence data from previous phylogenetic studies. Fresh green leaves collected in Guangxi were preserved in silica gel, and total genomic DNA was extracted using a modified CTAB method. The resulting concatenated dataset comprised 61 sequences representing 55 species from three genera of Celastraceae, with the genera Tripterygium and Celastrus serving as outgroups. All sequences other than those newly generated for E. saxatilis and E. maotaiensis were retrieved from the NCBI GenBank database.
The phylogenetic analysis was carried out in PhyloSuite v1.2.3, with sequences aligned in MAFFT v.7.475 using default parameters and ambiguous, low-quality alignment sites trimmed with trimAl before concatenation. The best-fit partition scheme and nucleotide substitution models were selected through the built-in ModelFinder under the Bayesian Information Criterion, assigning the GTR+F+I+G4 model to the ITS partition and the K3Pu+F+G4 model to the trnL-F partition. Maximum likelihood analysis was performed in IQ-TREE with bootstrap support estimated from 1,000 replicates. The result placed all accessions of E. saxatilis in a monophyletic lineage with maximum nodal support, resolved as sister to E. dielsianus with strong bootstrap support of 98 percent, corroborating the recognition of the new species.
The broader tree also carried a message about classification within the genus. Only species of Euonymus sect. Uniloculares formed a highly supported monophyletic clade, with bootstrap support of 100 percent, whereas species from all other sections were intermixed across the tree, a pattern largely congruent with previous studies. This matters because traditional infrageneric classification in Euonymus has relied heavily on fruit characters, a practice dating back to Blume in 1827, who first divided the genus into two sections based on fruit morphology. In the Flora Reipublicae Popularis Sinicae, the genus was subdivided into five sections distinguished mainly by capsule form: sect. Uniloculares with winged capsules and unilocular anthers, sect. Melanocarya with capsules four-lobed almost to the base, sect. Echinococcus with capsules armed with spines or tubercles, sect. Ilicifolii with smooth, suborbicular or globose capsules, and sect. Euonymus with usually rugose capsules bearing costae.
Molecular phylogenetics has complicated that fruit-based system, and the closely related genus Glyptopetalum illustrates the tension. Some taxonomists treated Glyptopetalum as a distinct genus on morphological grounds, while others omitted it or recognized it as an infrageneric taxon within Euonymus. In recent studies describing new species such as E. aquifolium, E. chengduanus, and E. maotaiensis, Glyptopetalum was consistently found nested within the Euonymus clade, and a numerical taxonomic analysis further supported reducing it to a section of Euonymus. The present study accordingly adopts a broad circumscription of Euonymus, treating Glyptopetalum as E. sect. Glyptopetalum, and the authors note that future work should combine a broader suite of morphological characters with multi-locus molecular markers to refine the sectional classification.
Integrating the species’ core diagnostic feature of deeply lobed capsules with its phylogenetic placement, the authors assign E. saxatilis to E. sect. Melanocarya. The species’ habitat may explain several of its traits: it occurs predominantly on the middle to upper slopes of karst peak clusters, and its thick, coriaceous leaves are interpreted as a typical adaptation to the locally arid conditions, reducing water transpiration, while the relatively large leaf dimensions are suggested to enhance light capture in an environment of high light availability and nutrient-poor soils. Because the vast majority of Celastraceae species are primarily insect-pollinated, the authors also infer that the larger floral structures and longer filaments of E. saxatilis may enhance its attractiveness to pollinators and improve pollen dispersal efficiency. The specific epithet derives from the species’ typical karst landform habitat, and the Chinese vernacular name is Yan sheng wei mao.
The known range of the new species is strikingly restricted. Euonymus saxatilis has so far been found only at a single wild locality within Mulun National Nature Reserve, where approximately 20 individuals were counted, all confined to the middle to upper sections of karst mountainsides at around 750 meters elevation. Given this extremely narrow distribution, small population size, and restriction to a specialized, narrowly endemic karst habitat, the species has been assessed as Critically Endangered under the IUCN categories and criteria. The type specimen was collected at Chuanshan Town in Huanjiang Maonan Autonomous County on 5 July 2025 and deposited in the GZAC herbarium, and the newly generated sequences have been deposited in GenBank, providing the morphological and molecular baseline for future studies of this newly recognized karst endemic.
Subject of Research: Description of a new plant species, Euonymus saxatilis, from karst habitat in Guangxi, China, based on morphology and molecular phylogenetics
Article Title: Euonymus saxatilis ( Celastraceae ), a new species from karst regions in Southwest China
Article References: Qiu, J., Wu, X., An, M.-T., Yu, J.-H., & Li, G.-L. (2026). Euonymus saxatilis (Celastraceae), a new species from karst regions in Southwest China. PhytoKeys, 280, 249-261. https://doi.org/10.3897/phytokeys.280.195001
Image Credits: AI Generated
DOI: 10.3897/phytokeys.280.195001
Keywords: Euonymus saxatilis, Celastraceae, new species, karst, Guangxi, China, phylogenetics, ITS, trnL-F, taxonomy, Mulun National Nature Reserve, Critically Endangered
News Source: Drew Townsend. (October 28, 2026). New karst-dwelling shrub Euonymus saxatilis described from Guangxi, China. Scienmag.
