Jan superbly covered this topic, and thanks for clarifying the history of D. indica.
<<Do you know why? It was Barry Meyers-Rice that proved that these now separate species cannot be hybridized. Since a species is a breeding pool and the different forms of Byblis cannot interbreed, they must then be iron clad separate species. This case of Byblis has more of a mathematical exactness of true science. >>
<Not really..........The case of _D. tokaiensis_ is exactly as obvious and simple genetically and taxonomically, and still some people would rather treat it as an independent species just because it is *not* sterile.>
How about the offsprings? To be recognized as its own species, I thought offsprings should not segregate as you often see those of primary hybrids. I was thinking the case of D. anglica, and that may be relevant as well, right?
<The important point (that has obviously still not penetrated public awareness sufficiently) is that sterility, fertility, and breedingbehaviour *alone* are *not* sufficient (although these data are doubtlessly useful) for species delimitation in many cases, especially not in the genus _Drosera_ (or _Nepenthes_ or _Sarracenia_).>
I agree. I think sterility among hybrids simply shows genetic dustance(s) between two parental species.
<Splitting and lumping will continue irrespective of the methods used.>
Speaking of sterility (or fertility) among primary hybrids, many of (not all, though) orchid primary hybrids are perfectly fertile. Intergenerics (hybrids between different genera) are hardly new. You can buy hybrids of Brassolaeliocattleya (Brassavola x Laelia x Cattleya), Ascocenda (Ascocentrum x Vanda) and Vulystekeara (Miltonia x Cochlioda x Odontoglossum) even at local Lowes (or Home Depot). If I remember correctly, there is a man-made genus that consists of species from nine genera. Of course, this depends on species, genera, subtribes, and tribes that orchids belong to. The concept of species that is readily applied to a group of family/genus, etc may not be applicable to another.
<Only the inclusivity of taxonomic ranks is defined (a species cannot contain two different genera but a genus can contain two different species),>Does this apply to fungal species as well? For example, Giberella fujikuroi is a teleomorph of Fusarium moniliforme (anamorph). I remember some macrocyclic rust fugi belonging to three genus depending on the number of life cycles. Since this is fungal taxonomy, the situation may be different.