A sleek, green-mottled frog collected on rocks beside mountain streams near the China–Myanmar border has turned out to be a species new to science. In a study combining DNA sequencing with detailed morphological examination, researchers describe Odorrana sudianensis, a new odorous frog from Sudian Town in Yingjiang County, Yunnan Province, China. The same analyses also confirmed the first national records of a second species, Odorrana heatwolei, in Thailand and Vietnam, extending the known range of a frog previously documented only from Laos and southwestern China.
The genus Odorrana, commonly known as odorous frogs, belongs to the family Ranidae and is one of the most species-rich amphibian genera in Asia, with members distributed from Japan and southern China through north-eastern India and mainland Southeast Asia to Malaysia and Indonesia. Sixty-seven species are currently recognised, 45 of them documented in China, making the country a global hotspot for the group. Yet the genus has long frustrated taxonomists: most species are morphologically conservative, meaning their outward appearance offers few reliable clues for telling them apart. Over the past decade, 14 new species have been described, and the authors of the new study argue that diversity within the genus remains significantly underestimated.
The trail began during field surveys in Yingjiang County, where two Odorrana specimens could not be assigned to any known species. Separately, three tissue samples had been collected during earlier expeditions in Nan and Phitsanulok Provinces in northern Thailand, and four additional samples, including one whole specimen, came from Dien Bien Province in north-western Vietnam. The specimens were photographed, humanely euthanised, and preserved as vouchers at institutions including the Kunming Institute of Zoology, the Field Museum of Natural History, the University of Kansas and the University of Phayao, with research protocols approved by the institute’s ethics committee.
To resolve the specimens’ identities, the team extracted genomic DNA from muscle or liver tissue and amplified a fragment of the mitochondrial 16S ribosomal RNA gene, a workhorse marker in amphibian species delimitation. They assembled a matrix of 97 sequences spanning 665 base pairs, including 87 homologous Odorrana sequences from GenBank and three outgroup taxa, and deliberately prioritised sequences derived from holotypes, paratypes or topotypes wherever possible so that the true clades of the genus could be anchored to named material. Phylogenetic trees were inferred with both Maximum Likelihood, using 1,000 bootstrap replicates, and Bayesian Inference, run for ten million generations, and the two methods recovered largely congruent topologies with relatively high nodal support.
The results were unambiguous for the Yingjiang frogs. The two specimens from Sudian clustered within a monophyletic Odorrana as a deeply divergent, undescribed lineage, recovered as the sister taxon of O. dulongensis, a species described from Dulongjiang Village in Gongshan County, Yunnan, with strong support (Bayesian posterior probability of 1 and bootstrap support of 95). The mean uncorrected p-distance between the Sudian population and O. dulongensis, based on the 16S gene, was 4.6 percent, exceeding the threshold typically required for amphibian species delimitation. Combined with differences in colouration, skin texture and body proportions, the genetic evidence justified formal description of the new species.
Odorrana sudianensis is a robust, medium-sized frog known only from two adult females, with snout-vent lengths of 78.9 to 85.3 millimetres. Its diagnostic traits include a head longer than wide, an iris bearing intricate golden reticulations that form a circumpupillary ring, a dorsum mottled grass-green in front with dark brown blotches behind, absent dorsolateral folds, distinct dark brown crossbands on the limbs, a deeply notched cordiform tongue, and significantly expanded finger discs with circummarginal and lateroventral grooves. The specific epithet sudianensis honours the type locality, and the authors propose Sudian odorous frog as the English common name. The holotype, an adult female, was collected in December 2024 at 1,563 metres above sea level, with a paratype from the same area taken the previous September.
The species was found on rocks under shrubs along riverbeds and mountain streams at roughly 1,600 metres elevation, sharing its habitat with O. yunnanensis, Leptobrachella yingjiangensis, Megophrys sp., Jingophrys feii and Amolops afghanus. In comparisons, the new species differs from its sister species O. dulongensis in flank colouration, ventral markings, the supratympanic fold, supernumerary tubercles and relative finger lengths, and it can be separated from a long list of congeners, including O. yunnanensis, O. margaretae, O. kuangwuensis, O. jingdongensis, O. grahami, O. junlianensis, O. mutschmanni and O. wuchuanensis, by combinations of body size, colour pattern, skin texture and finger proportions. The authors note the limitation that only two female specimens were available, so morphological comparisons were restricted to female characters documented for the taxa included.
The second major finding concerned O. heatwolei, Heatwole’s odorous frog, originally described in 2005 from the Nam Ou River in Phou Dendin National Biodiversity Conservation Area, Phongsaly Province, Laos, and later reported from Xishuangbanna in Yunnan, China. The species’ history has been turbulent: in 2007 it was placed under the synonymy of O. tiannanensis, a decision later challenged and reversed by other researchers using molecular data, which identified O. heatwolei as the sister taxon of O. tiannanensis. In the new analyses, the seven samples from Thailand and Vietnam clustered strongly with type sequences of O. heatwolei (posterior probability of 1, bootstrap support of 100), with pairwise divergences of less than 1.0 percent from the holotype, compared with 2.8 to 5.7 percent from topotypic O. tiannanensis sequences, confirming the first national records for Thailand and Vietnam.
The Vietnamese specimen examined, an adult male with a snout-vent length of 50.8 millimetres, was collected in January 2019 at 700 metres elevation in Dien Bien Province near the Laos border. Its morphology aligns closely with the male holotype from Laos and male specimens from Yunnan in all key adult diagnostic traits, including body size, tympanum visibility, dorsal skin texture and the presence of dorsolateral folds, with slight differences in colouration likely reflecting age, regional or habitat-related variation rather than taxonomic distinction. The species inhabits forest streams and river banks between 600 and 1,200 metres, favouring low-gradient rocky streams bordered by dense broadleaf forest, and specimens in nocturnal surveys were found on low vegetation or rocks near flowing water, suggesting a strong association with riparian zones. With the new records, the number of Odorrana species known from Thailand rises to seven and from Vietnam to 23.
The study also untangled several other taxonomic knots. Sequences previously submitted from northern Vietnam as O. bacboensis were recovered within the true O. bacboensis subclade, supporting the presence of that species in both mainland China and Vietnam. Samples from northern Vietnam attributed to O. fengkaiensis fell within that species’ subclade, while O. hainanensis was confirmed as a closely related but distinct lineage. Topotypic sequences of O. hejiangensis and O. nanjiangensis formed the same strongly supported subclade, with a reported genetic distance of just 0.1 percent, leading the authors to propose synonymising O. nanjiangensis with the senior O. hejiangensis, pending examination of voucher specimens. Their analyses did not support the proposed synonymy of O. jingdongensis and O. hmongorum, a weakly supported species group that earlier work has shown to be complicated by mitochondrial introgression and mitonuclear discordance.
With the addition of O. sudianensis, the genus now numbers 67 species, 46 of them known from China. The authors emphasise that the findings underscore how much amphibian diversity in the Indo-Burma biodiversity hotspot remains hidden, and that further surveys in the northern and north-eastern border areas of Thailand and in northern and central Laos and Vietnam are likely to uncover additional populations. They call for integrative approaches combining extensive sampling, genome-wide sequence data, morphology and bioacoustics to delimit species boundaries accurately, not only within Odorrana but across other amphibian genera, and to strengthen conservation measures for the region’s amphibians. For now, the Sudian odorous frog is known only from its type locality, a reminder of how much still awaits discovery along these forested border streams.
Subject of Research: Description of a new odorous frog species from Yunnan, China and new national records of Odorrana heatwolei in Thailand and Vietnam
Article Title: Unveiling hidden diversity in Odorrana ( Anura , Ranidae ) with description of a new species from Yingjiang, China and the first national records of Odorrana heatwolei in Thailand and Vietnam
Article References: Kilunda, F. K., Yang, S.-P., Nguyen, L. T., Le, M. V., Suwannapoom, C., Stuart, B. L., Nguyen, S. N., Zuo, A.-R., Zhang, D.-C., Duan, Z.-P., Duan, P.-W., Yu, Z.-B., Wu, Y.-H., & Che, J. (2025). Unveiling hidden diversity in Odorrana (Anura, Ranidae) with description of a new species from Yingjiang, China and the first national records of Odorrana heatwolei in Thailand and Vietnam. Zoosystematics and Evolution, 101(4), 2337-2356. https://doi.org/10.3897/zse.101.162366
Image Credits: AI Generated
Keywords: Odorrana, Odorrana sudianensis, Odorrana heatwolei, amphibians, integrative taxonomy, new species, Yunnan, Thailand, Vietnam, 16S rRNA, phylogenetics, Indo-Burma
News Source: Margaret Porter. (October 26, 2026). New odorous frog species emerges from China’s borderlands as Heatwole’s frog turns up in Thailand and Vietnam. Scienmag.
