Some clarification why I don't think cladistics is going to have much effect on lower taxonomic levels. Plants in a single genus usually have a close phylogenetic relationship, i. e. they evolved from a common ancestor. Plants in a single family usually have a close phylogenetic relationship, i. e. they evolved from a common ancestor. So it seems to me that this is consistent with cladistics.
I offer the following quote from Wikipedia in support of the above statements. (
Cladistics - Wikipedia)
Since the early 20th century, Linnaean taxonomists have generally attempted to make at least family- and lower-level taxa (i.e. those regulated by the codes of nomenclature) monophyletic.
A monophyletic group is one which evolved from a common ancestor. Thus we see that under the Linnaean system of taxonomy a basis for a cladistic interpretation is in place at the lower taxonomic levels, although there are probably some exceptions.
Despite the growing popularity of cladistics, the traditional Linnaean
system is not likely to be replaced in the near future.
More info here:
PhyloCode - Wikipedia
Edited by penstemo, : More info added
Edited by penstemo, : Added more info