Molecular phylogeny of the genus Asparagus (Asparagaceae) inferred from plastid petB intron and petD-rpoA intergenic spacer sequences

Asparagus (Asparagaceae) is a large genus that is widely distributed in arid and subarid regions of the Old World. To investigate the phylogenetic relationships within this genus, the intron of petB and the intergenic region between petD and rpoA of chloroplast DNA (cpDNA) were sequenced. A strict consensus tree resulting from the phylogenetic analysis indicates that southern African species comprise a potentially paraphyletic assemblage and that Eurasian species are monophyletic. This result suggests that the genus Asparagus originated in southern Africa, and that Eurasian species originated from a southern African progenitor. Moreover, extensive survey of the intergenic region between trnL and trnF and the intron of trnL of cpDNA in species of the genus Asparagus displayed no sequence differences despite the non-coding regions frequently used to reconstruct intrageneric phylogenies. Therefore, we hypothesized that rapid radiation of this genus might have been influenced by the gaining of unique characteristics, such as phylloclades, in order to adapt to the dry environment.