Phylogenetic correctness

It is axiomatic to state that grasslands are dominated by grasses. It is also axiomatic to state that the trait that allows grasses to dominate grasslands is an adaptation to the grassland environment. The identities of the traits are currently unclear. For example, meristem position used to be the oft-cited reason for grass dominance, despite the clear evidence of many less abundant eudicots with similar meristem position. Yet, whenever we discover what the trait is that separates grasses from other species and allows them to dominate grasslands, we will never be able to declare that trait an adaptation. Such is that state of phylogenetic correctness.

There are many important traits that arose only once. True wood, angiosperm xylem vessels, and Rubisco likely only evolved once and cannot be separated from phylogenetic origins. The conditions and the complexity of the trait did not lead to multiple origins, but instead served as the basis of radiations. Any trait that sits at the base of a tree cannot officially be considered an adaptation. Even if a trait had arisen twice, there would be no statistical basis for calling something an adaptation since it cannot be separated from phylogeny.

What are we left with then? We can apply phylogenetic corrections to account for relatedness when examining trait relationships, and it provides useful knowledge. But to what ultimate point if phylogenetic corrections will not ultimately rule out or in something as an adaptation.

It's currently a silent sticky point in our considerations of the evolution and ecology of plants. One to which I don't have a complete answer, but one of which would be helpful to have clearer consideration. In the end, we will likely determine how grasses differ from other species and why they come to dominate what we call grasslands. And when we do, it'd be nice to be able to recognize the adaptations of grasses for what they are.