Speciation is the process of formation of a new species from the existing ones. When a population of species splits into groups and gets separated due to geographical barriers, speciation occurs. There is a lack of gene flow between the separated species. This leads to reproductive isolation. Variations occur in isolated species to adapt to their surroundings, which are inherited over generations. After many generations, these species show great variations and develop into a completely new species which cannot reproduce with each other. Yes, geographical isolation is a major factor in the speciation of self-pollinating plant species. In plants that reproduce by self pollination, variations arise due to mutation and natural selection. They modify and adapt themselves to survive in the given environment. Thus, two groups of plants of the same species living in different environmental conditions will form two new and different species after many generations and lead to speciation.