DNA homology as a tool for determination of divergence of phanerogamic taxa

Abstract

The utility of DNA homology as tool for determination of divergence of phanerogamic taxa is discussed. DNA-DNA hybridization values of living gymnosperms and members of primitive angiospermic families indicate highest homology between Gnetum and Magnoliaceae, supporting the gnetalean origin of angiosperms. Conifers like Thuja occidentalis show no less homology with primitive angiosperm families than do the cycads. The living monocots and gymnosperms have diverged even farther. The primitive dicotyledonous families revealed fairly high homology among themselves but the other more derived families have diverged appreciably. The DNA homology among the primitive dicots and monocots varied between 45 and 60 per cent. With respect to the more advanced families, the homology values decreased. Families at moderate levels of evolutionary advancement exhibit intermediate values when compared. The two major groups of angiosperms seem to have evolved along parallel lines from a common stock in the remote past.