In: Phyton 60, Fasc. (2020): S. 173-221; DOI: 10.12905/0380.phyton60-2020-0173; Published online on 23 December 2020

Taxonomic revision of the Spiraea japonica complex (Rosaceae)

Roman Businský

with 7 figures

Key words: Rosaceae, Spiraea, Spiraea naxiorum spec. nova, Spiraea celtifolia spec. nova, Spiraea japonica var. vulcanica var. nova, Spiraea ovalifolia stat. nov., Spiraea japonica var. kweichowensis comb. nova et stat. nov., Spiraea morrisonicola var. hayatana comb. nova et stat. nov. – Taxonomy, synonymy, typifications. – Flora of Japan, China, Himalayas and adjacent regions.

Summary
Businský R. 2020. Taxonomic revision of the Spiraea japonica complex (Rosaceae). – Phyton (Horn, Austria) 60: 173–221, with 7 figures.*
The aim of this treatise is to present all available information relevant to the taxonomic classification of the group of morphologically similar taxa believed to be related to the widely variable species Spiraea japonica L. f., which is native to SE Asia and commonly cultivated around the world. After careful taxonomic revision of all Spiraea taxa with terminal compound corymbs, this group, called here the S. japonica complex (accepted in a much broader sense than it was previously used), was found to comprise at least ten species. Two other species, S. fritschiana C. K. Schneid. and S. ovalifolia (Franch.) Businský, remain in uncertain position; the morphology of these two species lies between that of the S. japonica complex and the S. betulifolia aggregate. The revision is based on a field study of nine species from those accepted here and on an extensive examination of hundreds of herbarium specimens of all involved taxa from original collections as well as available recent representative material. Among the ten species of the complex, S. japonica proper is formed by nine varieties (of which var. vulcanica, locally endemic in westernmost Yunnan, China, near the border of Myanmar, is newly described), and the Taiwanese S. morrisonicola Hayata consists of two varieties (with S. morrisonicola var. hayatana as the newly combined variety). Of the eight remaining species, S. naxiorum (native to the mountains of a relatively small area in SW China) and S. celtifolia (from the borderland of the Chinese region Xizang and Nepal and known further east to NW Yunnan) are described as new species. Two other new taxonomic changes are proposed: S. kweichowensis T. T. Yu & L. T. Lu is relegated to a variety of S. japonica, and S. japonica var. ovalifolia Franch. is elevated to the rank of species as S. ovalifolia. The nomenclatural types of all accepted taxa and taxonomic synonyms are identified, many as newly designated lectotypes (24 items, two supported by epitypes) or neotypes (4 items).