Cladogenesis is a pattern in
evolution in which
two or more groups in a
population of a single
species start to
differentiate and give rise to new species.
The rise of cereal crops (oats, barley, rye and wheat) from a common ancestor is an example of cladogenesis. Features that prevented interbreeding between the sub-populations evolved first, and then further speciation occurred.
Compare anagenesis.
For more information: http://www.ndsu.nodak.edu/instruct/mcclean/plsc431/popgen/popgen6.htm