Section 'Subdivisions' should be more than a list. 

I hate to complain about a problem, rather than just fix the problem, but I really don't know enough about biology to be productive here.

The Problem: I read eudicots, rosids, and asterids.  Although each article lists some representative species, I (the reader) have no understanding what criteria was used to subdivide eudicots into rosids and asterids (and others).  Why is one plant a rosid but not an asterid?  These articles read as though plant life is subdivided arbitrarily, though I suspect the subdivision is somewhat rational.  My intuition tells me that there must be some expressible, meaningful distinction between these subgroups.

The Proposal: Is there some way to describe the grouping here?   I propose a brief summary of the characteristics which divide rosids and asterids.  I think this summary should be a list of differences, each difference taking this form:
 Rosids feature X.  In contrast, Asterids feature Y.

Thanks, 71.63.4.110