Systematic and evolutionary implications of rbcL sequence variation in Rosaceae

TLDR: RbcL-based phylogenies suggest that chromosome numbers are more reliable indicators of some generic alliances than the more commonly used fruit types and that the subfamily Maloideae may have descended from spiraeoid ancestors and the pome is derived from follicular or capsular fruit types.

Abstract: The angiosperm family Rosaceae poses a number of noteworthy systematic problems as well as many questions concerning morphological and chromosomal evolution. Phylogenetic analysis of rbcL gene sequences was performed to address systematic and evolutionary problems of Rosaceae. Both rbcL sequence variation and the presence of duplicated sequences near the 3' end of rbcL were useful in determining phylogenetic relationships in this family. Analyses of rbcL sequences indicate that there are groups of genera within Rosaceae comparable to the subfamilies Maloideae, Amygdaloideae, and Rosoideae, although the composition of each group differs from traditional circumscriptions. According to analysis of rbcL data, Maloideae and Amygdaloideae each include additional taxa not normally associated with them. All members of Rosoideae with x = 9 are phylogenetically well separated from the x = 8 and 7 members of the subfamily. In addition, Spiraeoideae are not monophyletic but appear to consist of several distinct evolutionary lineages. The rbcL-based phylogenies suggest that chromosome numbers are more reliable indicators of some generic alliances than the more commonly used fruit types. Sequence data are also useful in determining the alliances of several problematic genera, suggesting that the capsular and follicular-fruited genera Vauquelinia, Lindleya, and Kageneckia (usually placed in Spiraeoideae) should be included in the pome-fruited subfamily Maloideae, and that Quillaja is not a member of Rosaceae. Molecular data are consistent with several suggestions for the ancestral chromosome numbers and fruit types of Rosaceae, but do not support any one hypothesis for either. This study also suggests that the subfamily Maloideae may have descended from spiraeoid ancestors and that the pome is derived from follicular or capsular fruit types.