Discontinuous DNA variation in the evolution of plant species

The four genera,Clarkia, Nicotiana, Lathyrus andAllium have widely different geographical distributions and evolutionary patterns, but the nucleardna amounts of species within each genus occur in groups at intervals of approximately 2 or 4 picograms. Diploids with different basic chromosome numbers, and polyploids, can occur in the same group. When anydna group of one genus is paired with the nearestdna group of another genus all other groups of both genera pair exactly in so far as they have a common range of DNA amounts. Hence thedna groups of the four genera are associated in larger groups, or nodes, separated by 2 or 4 picograms forming a progression over all four genera, implying there are favoured, discontinuous,dna amounts, either arisingde novo or subsequently within a continuously varying distribution.