Taxonomic revision of the Spiraea longigemmis complex (Rosaceae)

The aim of this treatise is to revise the taxonomic classification of the `Spiraea longigemmis complex', a group of morphologically similar taxa with compound corymbs on short lateral branchlets, bisexual flowers, stamens much longer than the petals, and homomorphic, more or less doubly serrate leaf blades. Members of this group are mostly distributed in China and were presented in both editions of the `Flora of China', however, following the faulty historical species con-cept based on the limited herbarium material, though later enriched by abundant collections, yet often incorrectly identi-fied. A new classification of this group, based on a field study of relevant populations, on extensive examination of abun-dant material from various herbaria worldwide and on comparison with the original literature, is proposed in the present treatment. The revised S. longigemmis complex comprises five species and one interspecific hybrid native to China, and one species native to Japan and North Korea. Spiraea rosthornii E. Pritz. ex Diels is the most widely distributed species in the complex, occupying a nearly 2000-km-long range across Central and Southeast China. The newly described vari-ety S. rosthornii var. ombrophila was discovered ca. 600 km eastward of this range in a very limited area in southeastern Xizang (interior Tibet, China). Three Chinese varieties ascribed to the Japanese S. miyabei KkoiDz. by RrehDer in 1913 are synonymized with S. hingshanensis T. T. Yu & Ll. t. lu and with each other. The new species S. fornicata, confused with several taxa since the 1970s, is described from southeastern Xizang. The extensive distribution area of a hybrid complex, evolved from the supposed hybridization of S. fornicata and S. longigemmis, was detected in the Tibetan mountain region of the Chinese provinces Sichuan and Yunnan and identified with the old name S. prattii C. K. SschneiD. Abundant her-barium material ascribed here to the `S. xprattii hybrid complex' was examined in herbaria within and outside China, consisting of specimens filed under at least six species names. The nomenclatural types of all accepted taxa and their taxonomic synonyms are identified, six as newly designated lectotypes. The lectotype of S. miyabei and the holotype of S. hingshanensis are supported by epitypes.