Taxonomy and phylogeny of the intercontinental disjunctive ferns: series Reniformia Adiantum

There are disputed opinions about the three taxa of series Reniformia , namely A. nelumboides X.C.Zhang ( A. reniforme var. sinense Y.X.Lin), A. reniforme var. reniforme , and A. reniforme var. asarifolium (Willd.) R. Sim, owing to their similar morphology but intercontinental disjunctive distribution and close lineage with the series Venusta (only distributed in China). In order to clarify their relationship, we studied their morphological characteristics and conducted phylogenetic analyses of Adiantum including the series Reniformia and series Venusta . The results showed that A. reniforme var. asarifolium diverged before A. reniforme var. reniforme and A. nelumboides , and A. flabellum had a close relationship with A. nelumboides . Distinctive morphological features were determined to help identification. All these suggested that A. nelumboides , A. reniforme var. reniforme , and A. reniforme var. asarifolium were three independent species rather than varieties. Therefore, we propose that A. reniforme var. asarifolium is a synonym of A. asarifolium and support that A. reniforme var. sinense is a synonym of A. nelumboides . Furthermore, the voucher plate (type specimen) of Adiantum reniforme var. asarifolium did not match its description in the original publication, and the specimen (no. 2444215 in MO) in Kenya may be A. nelumboides , and there are some other disputed taxa around the Madagascar Islands. Results from haplotype analyses and genetic diversity indicated that genetic differentiation among these taxa was increased by long periods of geographical isolation. China was deduced to be the most possible original evolution center of series Reniformia ; areas along the southeast coast of Africa (Madagascar, Mauritius, Kenya, and Réunion) were the genetic diversity centers of the modern series Reniformia . The Canary Islands/Madeira was inferred to be the glacial refugia of A. reniforme var. reniforme in the western Mediterranean during the late Quaternary.