ABSTRACT
The notion of species is the cornerstone of systematic botany as well as of biology or biodiversity studies. The species is also a fundamental unit for ecologists, agronomists, horticulturists, and specialists in the conservation and protection of nature. Practically and intuitively, taxonomists distinguish one species from another by different and stable morphological characteristics. The importance of reproduction in different species is obvious. It is the indispensable condition for perpetuation of the species through a succession of generations. Hybridization and introgression are frequent phenomena in plants. Generally, they represent a break or an inversion of processes of differentiation and thus speciation. Hybridogenic speciation has occurred directly from a natural hybrid by stabilization of reproductive behaviour of the hybrid and by reproductive isolation from the two parents. Hybridogenous speciation may be rapid and it can be shown experimentally that in 60 generations of Helianthus, we can end up with one speciation per recombination.
