Multiple sources of evidence unravel a complex taxonomic history: the new genus Leonoria of the Spermacoce clade (Spermacoceae-Rubiaceae)

Abstract

For a long time, the taxonomic status of Denscantia, a genus endemic to the Atlantic Forest along the Brazilian coast, has been a topic of discussion. Phylogenetic analyses using two nuclear and four chloroplast DNA markers from 82 accessions representing 19 genera of the Spermacoce clade (tribe Spermacoceae, Rubiaceae) confirm that the Brazilian genus Denscantia is biphyletic. Together with the recovered phylogenetic relationships, the analyses of reproductive morphological characters, leaf morphology and anatomy, histochemical, geographic distribution ranges, and ecological niche derived from climatic space further demonstrate that Denscantia calcicola is a distinct lineage from the other Denscantia species. Therefore, the above-mentioned species should be taxonomically designated as a new monospecific genus, Leonoria. Significant morphological differences between Leonoria and Denscantia were found in inflorescence organization, style shape, fruit dehiscence and pollen morphology. Morphological and anatomical variation among leaf traits was found in epidermal cells, trichome distribution, mesophyll histochemistry and vascular organization. The analysis of occurrence records of 207 specimens demonstrates a clear ecological distinction between of Denscantia s.s. and Leonoria, which is ecologically confined to limestone outcrops associated with seasonally dry forests. The current study highlights the importance of an integrative taxonomic approach combining multiple sources of evidence to unravel complex taxonomic history within Spermacoceae.