Relations and evolution in Cheilanthes (Sinopteridaceae, Pteridophita) in Macaronesia and Mediterranean area, deduced from genome analysis of their hybrids

Abstract

Nine species of "Cheilantoid ferns" are known to grow in Macaronesia and the Mediterranean basin. Two of them (lacking a pseudo-indusium and having the basic chromosome number X = 29), both aggregate species which we prefer to retain in Notholaena, are not included in this study. The other seven species (with distinct pseudo-indusium and the basic chromosome number X = 30), which we accept as members of the genus Cheilanthes Sw. sensu stricto, were subjected to detailed genome analysis of their natural and experimentally produced hybrids and shown to represent an aggregate of four very distinct ancestral diploids and three allotetraploids. The latter must have once been formed by chromosome doubling in the three diploid hybrids of C. maderensis Lowe with the other three diploid species. Theoretically three more allotetraploids would be possible but their formation has obviously been prevented by the geographical separation of the three respective diploids. The most widely distributed of the tetraploids, i.e. C. pteridioides (Reich.) C.Chr. has also been resynthesized from its ancestors (still sympatric) under experimental conditions. The intermediate morphology of the allotetraploids (as compared with their diploid ancestors) is obviously the reason why their status and existence has so long escaped recognition in Europe. These seven species form a natural group and, in our opinion, should not be divided into sections.