What is sympatric speciation?
It involves the splitting of an ancestral species into two or more reproductively isolated groups without geographical isolation of those groups. The key aspect of sympatric speciation is that it occurs when incipient species are in physical contact with each other, potentially able to interbreed and exchange genes.
It is one of the three traditional geographical modes of speciation. Here there is no geographical constraint to interbreeding. Sympatric speciation is unique because the process begins with complete genetic mixing between the diverging groups.
Sympatric speciation events are quite common in plants, which are prone to acquiring multiple homologous sets of chromosomes resulting in polyploidy.