Cladogenesis is a pattern in evolution
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.
For more information: http://www.ndsu.nodak.edu/instruct/mcclean/plsc431/popgen/popgen6.htm