Hybrids can be readily made, but as with most hybrids they are sterile. This kind of thing is relatively easy to show in plants, because of their ease of hybridization. It is estimated that up to 40% of existing plants species have arisen by this mechanism.
Now, here's what you're looking for: after many thousands or millions of hybrids, a chromosomal rearrangement will occur that will allow the "hybrid" to be fertile. But it is never fertile with either of the "parents" of the hybrid. IOW it is no longer a hybrid but an entirely new species with a completely different complement of genes.
I don't doubt for a moment that it is possible for new species to come about. It may simply be that the biological entity was genetically programmed to manifest varitions we can only categorize as such. But what will be the limits of this variation? As far as I know, recorded history has fairly well attested to consistent results as life goes on. It is not a crazy stretch for anyone to conclude those plants were designed that way.