Phylogenetic relationships in the genus Asparagus based on the restriction enzyme analysis of the chloroplast DNA

Asparagus officinalis is important horticultural species. Genus Asparagus includes some ornamental species and some medicinally important species, and distributed on dry land in the Old World. To clarify the phylogenetic relationships within this genus, we compared the restriction sites of chloroplast DNAs (ctDNAs) among ten species. A. officinalis, A. cochinchinensis, A. schoberioides, A. asparagoides, A. falcatus, A. macowanii, A. plumosus, A. scandens, A. virgatus and A. sprengeri. Phylogenetic relationships within this genus, derived from the ctDNA restriction sites, yielded values for interspecific divergence (100 x p) that ranged from 0.4 to 2.4. Compared to other groups, such as Zea (0.0 to 0.3) and Aegilops/Triticum (0.24 to 1.0), the species of Asparagus exhibited higher levels of variation in their ctDNA. A phylogenetic tree showed that the Asparagus species used in this study could be divided into two clusters. The phylogenetic relationships derived from variations in the ctDNA were slightly different from these proposed by Bailey (1944) and Clifford and Conran (1987). The ctDNAs of A. falcatus (tetraploid, 2n=40) and A. sprengeri (hexaploid, 2n=60) gave the same restriction pattern, indicating that these species are very closely related. Moreover, it is of considerable interest that the polyploid species of Asparagus were grouped in one cluster. The three dioecious species, A. officinalis, A. schoberioides and A. cochinchinensis, were also grouped into one cluster, which suggests the possibility that dioecy in Asparagus might have had a monophyletic origin.