Polyploid speciation and molecular evolution after genome duplication in the dwarf dogwoods
     The dwarf dogwoods (DW in Fig. 1) or bunchberries (Cornus Subg. Arctocrania) are perennial rhizomatous ground cover herbs, consisting of three species, C. canadensis L., C. suecica Lamark, and C. unalaschkensis Ledebour, closely related to the big-bracted dogwoods (BB in Fig. 1). The first two species are diploid (2N=22), and the third is a tetraploid (2N=44) (Bain & Denford, 1979). The three species are mainly distributed in areas of high latitudes and elevations of the Northern Hemisphere (Murrell, 1994). The tetraploid, C. unalaschkensis, is known to be restricted to the Pacific region of North America where the ranges of the two diploid species overlap and hybridize, resulting in a species complex consisting of two morphological extremes (corresponding to the two diploid species) and a wide array of intermediate forms combining different morphological features of the two morphological extremes (Bain & Denford, 1979; Murrell, 1994). The tetraploid species C. unalaschkensis, is characterized by bicolor petals, with the apical half purple and basal half cream (Fig. 1), while C. canadensis has white petals and C. suecica has dark purple petals. We use DNA markers and data from cytology to understand the origin and molecular evolution in the polylpoid species and the evolutionary history and processes of entire dwarf dogwood complex as a whole. The results of a study using an anthocynanin regulatory gene on the complex have been recently published (Fan et al. 2006). Other nuclear and chloroplast genes are being investigated.
Fig. 1. Dogwoods phylogeny inferred from molecular data