Chloroplast and nuclear evidence for multiple origins of polyploids and diploids of Hedera (Araliaceae) in the Mediterranean basin

Abstract

Chloroplast ( trnT–L) and nuclear rDNA (ITS) sequence analyses of the Araliaceae provide strong molecular evidence for the monophyly of the genus Hedera. Phylogenetic reconstructions suggest multiple origins and an active polyploidization process not only in the formation of tetraploids (2 n=96), hexaploids (2 n=144), and octoploids (2 n=192), but also of diploids (2 n=48). A high basic chromosome number of x=24, extensive polyphyly in widespread diploids, and terminal placement of Hedera in phylogenies of the Araliaceae reveal that extant diploid taxa may be, in fact, assemblages of ancestral polyploids from plants of n=12. Four major lineages containing four types of chloroplast (chlorotypes I, II, III, and IV), which are defined by different trnT–L nucleotide substitutions and two large insertions (50- and 30-bp), provide evidence for evolutionary processes and historical biogeography in Hedera. We propose a scenario where an initial colonization in the Mediterranean basin by Asian ancestors (carrying the ancestral Araliaceae chlorotype I) is followed by differentiation into the four chlorotypes of the Mediterranean region, and then recolonization of Asia and northern Europe only by chlorotype III. The Macaronesian taxa ( Hedera azorica, Hedera maderensis ssp. maderensis, and Hedera canariensis) appear to have originated from a single-colonization event to each archipelago with no further contact either with continental or insular species.