Scientific American, 22/2/89 wrote:Three species of wildflowers called goatsbeards were introduced to the United States from Europe shortly after the turn of the century. Within a few decades their populations expanded and began to encounter one another in the American West. Whenever mixed populations occurred, the specied interbred (hybridizing) producing sterile hybrid offspring. Suddenly, in the late forties two new species of goatsbeard appeared near Pullman, Washington. Although the new species were similar in appearance to the hybrids, they produced fertile offspring. The evolutionary process had created a separate species that could reproduce but not mate with the goatsbeard plants from which it had evolved.
There, species splitting separately and actually observed. There are no inbuilt limits saying these changes must stop at so and so a point or that the species cannot alter more than genetically, but also morphologically.
Should anyone dispute this, please cite a reference that shows with a certain degree of accuracy the limits that stop such speciation from taking place and I will happily retract my statements.