Defining clonality and individuals in plant evolution

Aarssen (2014) proposes estimating fitness in clonal and aclonal seed plants by defining an individual as a rooted-unit, which he defines by the root-to-shoot transition in anatomy of the stele. This approach may be helpful for some seed plant taxa, maybe even most seed plants, because of being much more readily operational than most other definitions of individuals. However, the rooted-unit approach seems to falter for many weird plants, such as those with anomalous root and shoot anatomy and plants that can reproduce clonally from leaves or apomictic seeds. Another problem with using rooted-units to circumscribe individuals is the implicit assumption that mitosis constrains genetic variance and meiosis increases genetic variance, when the exact opposite may be true. Although definitions of individuals are arbitrary, there may soon be sufficient data to ascertain which definitions are most useful, i.e. which definitions of individuals help unify evolutionary theory.