Phylogenetic reconstruction of Ficus subg. Synoecia and its allies (Moraceae), with implications on the origin of the climbing habit

The infrageneric classification of Ficus (Moraceae) has raised concerns since Berg put forward his six subgenera system. Molecular analyses have revealed some unnatural groups within this system. The status of F. subg. Synoecia and the relationships between this subgenus and its allies are among the major challenges facing classification within the genus. To resolve these problems, we reconstructed the phylogenetic trees with three nuclear markers from 147 ingroup taxa (including approximately half of F. subg. Synoecia species and three-fifths of F. subg. Ficus) and implemented ancestral area and life-form reconstructions to trace the evolutionary history. Results showed that F. subg. Synoecia and F. subg. Ficus (except F. subsect. Ficus) constituted a well-supported monophylum, which is sister to F. subg. Terega. This monophylum comprises two clades: one clade covers F. subsect. Frutescentiae of F. sect. Ficus and F. subsect. Plagiostigma of F. sect. Pogonotrophe, and the other covers F. sect. Eriosycea, F. sect. Apiosycea and the rest of F. sect. Pogonotrophe. Ancestral area reconstruction revealed that the first clade has a distinct origin in East Asia, but the second one shows fewer obvious signs. Ancestral life-form reconstruction suggested that the climbing habit, a key trait used to divide F. subg. Ficus and F. subg. Synoecia, has evolved independently more than four times, rendering it an unsuitable characteristic to circumscribe the subgenera. Thus, we merged F. subg. Synoecia and F. subg. Ficus (excluding F. subsect. Ficus) into one subgenus, containing two newly delimited sections and six new synonyms.