In: Phyton 55, Fasc. 1 (2015): S. 69-120 with 4 figures DOI: 10.12905/0380.phyton55(1)2015-0069

Transitive Inflorescence Types in Spiraea
(Rosaceae-Spiraeoideae) Undermine the Fundamental Classification Concept of the Genus
Key words: Rosaceae, Spiraea, Spiraea lanatissima spec. nova, S. ×transhimalaica, hybr. nova, varietates novae, Spiraeoideae. – Inflorescence morphology, taxonomy, typifications, variability. – Flora of Eurasia, E Asia.

Businský R. 2015. Transitive inflorescence types in Spiraea (Rosaceae-Spiraeoideae) undermine the fundamental classification concept of the genus. – Phyton (Horn, Austria) 55 (1): 69–120, with 4 figures.

Summary
The main aim of this study is to show that the concept of simple or branched pedicels that has long been used as the primary trait for species classification in the genus Spiraea is improper, at least in some species that form both types of pedicels, i. e. simple and compound inflorescences (corymbs). This finding undermines to a certain extent the basic classification of the genus, dividing species with simple or compound inflorescences as members of sections Chamaedryon and Calospira, respectively. Transitions between simple and compound inflorescence types exist within individuals of several Spiraea species. The occurrence of both morphological states in the Himalayan S. arcuata has led to its heterogeneous interpretation and seeming dual systematic position. The Chinese S. schneideriana and S. myrtilloides, described simultaneously in one publication based on limited herbarium material, represent two states of what is evidently one species: the latter, with typically simple corymbs, is accepted as a variety of the former [S. schneideriana var. myrtilloides (Rehder) Businský], with more or less compound corymbs. The neglected occurrence of occasionally branched pedicels was confirmed in the Chinese S. mollifolia, the Sino-Centralasian S. lasiocarpa and the Eurasian S. crenata, all of which have been described as only presenting simple corymbs. The Sino-Himalayan S. canescens, reported only with compound corymbs, forms an interspecific hybrid complex with S. lasiocarpa, showing conspicuous morphological variation in its extensive range in South-Central Xizang, where it has been misinterpreted as S. mollifolia. However, S. canescens was found to exhibit a partial occurrence of simple corymbs in several collections from localities where interspecific hybridisation is unlikely. The Japanese S. nipponica has long been known to form both types of inflorescences, but the simple type prevails, and it has therefore usually been classified into section Chamaedryon.

Four taxa are newly described here: Spiraea lanatissima Businský (as a member of the S. arcuata agg.), from a limited area in Western Sichuan; S. arcuata var. karnalica Businský, from Western Nepal; S. ×transhimalaica Businský (S. lasiocarpa × S. canescens), from South-Central Xizang; and S. mollifolia var. denudata Businský, from Western Hubei (but also known westward to Eastern Xizang), which has been confused with S. mollifolia var. glabrata (a synonym of S. arcuata). The Chinese taxon S. uratensis is newly synonymised with S. lasiocarpa because it represents an anomalous morphotype of the latter with poorly branched pedicels. Spiraea xizangensis from Central Xizang is relegated to a variety of Sino-Siberian S. alpina [S. alpina var. xizangensis (L. T. Lu) Businský], S. teretiuscula from southern Sichuan to a variety of the partly sympatric S. ovalis [S. ovalis var. teretiuscula (C. K. Schneid.) Businský]. All of the accepted taxa and their important taxonomic synonyms are typified, mostly with newly designated lectotypes. The lectotype of S. crenata, recently selected from the mixed Linnaean material, was found in conflict with the protologue and the current use of this name; thus, it was superseded by a new, corresponding lectotype selected from the same herbarium sheet.