A number of cases of disjunct distributions similar to the Liriodendron example are known from other plant species. You will see that in a phylogeny, species which are alive now are ONLY at the very ends of branches. The vertical branch lengths can be seen to approximately represent evolutionary change - the longer the branch the more change has occurred. Note that for any two species, in the time since they diverged, there will therefore have been change on EACH of the two branches which lead to them. Explain your answer.
Polyploidy is an important phenomenon in plant evolution.
Imagine a tetraploid species of sunflower that combines the genomes of two different species. Explain your answer. It was emphasized in lecture that ecological selection is an important force both in maintaining species cohesion and in the process of speciation. Species are adapted to distinct ecological niches and maintain their cohesion through selection for traits adaptive to their niche. Explain your answer.