A new species of Oriental-endemic Thalerosphyrus Eaton, 1881 (Ephemeroptera, Heptageniidae) from the Chinese Yunnan Oriental–Palaearctic transition zone and insights into cryptic diversity in the T. flowersi complex

The Ephemeropteran genus <i>Thalerosphyrus</i> Eaton, 1881 (Heptageniidae: Ecdyonurinae) is an Oriental-endemic genus hitherto comprising ten species, distributed from Sundaland to the Western Ghats of India and northeastern Indochina. Here, <i>Thalerosphyrus lannaae</i> <b>sp. nov</b>., belonging to the <i>T. sinuosus</i> group, is described from Yunnan Province (China), marking the northernmost record of the genus and extending its distribution into the Oriental-Palaearctic transitional zone. We also examined existing molecular data for <i>T. flowersi</i>, which revealed multiple deeply divergent lineages across India and Thailand, with the new species genetically closest to one of the Thai lineages. These findings highlight unrecognised cryptic diversity within the genus and underscore the need for taxonomic revision. An updated species key to <i>Thalerosphyrus</i> is provided. We discuss how larval preference for moderately cool, fast-flowing streams may explain the discovery of this tropically adapted Oriental-endemic genus in such high latitudes, and we explore the importance of transitional zones for aquatic insect diversity.