I'm working with plant species with weak reproductive barriers and find that some species contains organisms with different ploidy. I'm interested to know how the fact of different ploidy levels inside one species can be explained by the rights of botanical nomenclature and plant taxonomy.
Within the genus Geranium and Trifolium each polyploidy level is recognized as species.
See at the end of the attached paper. Hopefully you read German.
Article Staudengesellschaften mit Geranium sanguineum und Trifolium ...
I think that it depends on gene flow between races (in animals). If transition between different n is reversible and frequent enough to maintain common gene pool, they are not species. Conseptually sporophyte and gametophyte are same species with different ploydy level.
Dear Andrii
Within ferns different levels of polyploidy represent a reproductive barrier and each polyploidy level is recognized as species or at least as sub-species.
Yannis
Attached an interesting piece on the topic, arguing for the recognition of different ploidy levels as distinct taxa, and that addresses some of the nomenclature issues.
I suppose this has to be seen as a "case by case" situation.
In some plants the ploidy level does not lead to a separation of taxa.
Sometimes it adds to the over-expression of some genes (as in Emilia sp. - Asteraceae), or other outcomes.
In Tritichum aestivum (wheat) the ploidy variation does not incur in taxonomical changes because the metapopulations with different ploidy levels are not isolated in any way from the rest of the population. Some hexaploid cultivars of Tritichum produce larger plants and, therefore, are more desirable for human use.
Poliploidy is also common in other cultivars, like the common peanut (Arachis hypogaea) where you have some different basic ploidy numbers.
Other related Arachis species show the same pattern...
However a difference in ploidy could lead to a speciation process.
I still think this should be analysed in a case by case scenario.
Ploidy level is not necessarily a determining factor for speciation.
It would, I guess, depend on two principal things: (1) the nature of the polyploids, which could be anywhere between the extremes of allo- or auto-polyploid; and (2) the gene flow between ploidal races. If there is no gene flow, the races are different biological species and might be recognised as such. If the polyploid is allo-, then the genomic constitution of the polyploid differs from that of the diploid in containing an additional, distinct genome, and they may be recognised as different biological species.
But of course, because speciation is a continuous process we encounter every stage of speciation in nature, and it is not given in all cases where to draw a line between one species or several species.
In species complexes or complex species often different ploidy levels occurr. The mophology often is so complicated that no species can be recognised and the complex should be referred to as one species, with an explanation of the situation. However, chromosome counting as well as DNA study is necessary to reveal the true situation. FURTHER i agree with THOMAS Marcussen
Article First insights into the evolutionary history of the Davallia...
Thank all of you for helpful answers.
In my case I work with different birch spesies. They are very polymophic in morphological characters and also have wide rande of hybridization. Also a lot of differnt ploidy levels inside the genus - from 2x to 12x. But different chromosome numbers in this case can't be threated as strong reproductive barrier. I jut try to find the way how to solve many problems connected with the taxonomy and phylogeny of these plants.
Alas, the species category is a human invention. In nature we find all the transitions from an individual to a family. Therefore i think it is wise to categorise plants after their morphological characters. It is important that plants can be recognised. In more complex cases an explanation can be given, if necessary
Dear Andrii
It depending to the plant group. For example in Brassicaceae some species of the genera such as Alyssum, Thlasi, Lepidium showing the different cytotype.
In some group such as Ferns the cytotype is usually giving the new taxa, this problem come back to the mechanism of fecundation.
So, different cytotypes resulting to the new taxa but need more time and suitable ecological condition. Surely in DNA sequencing they will be segregate from each others.
Best Regards
A. A. Maassoumi
In general, yes, because different ploidy levels are not compatable genetically.
Basically the ploidy level is considered as a good criterion of a species-level distinction. However, as with all rules, in some cases this is not applied: for ex. Hoerandl [Taxon 58 (4), p. 1197] lumps 2x and 4x populations within the same (micro)species. I was also told (but I do not remember the details) that in some Compositae you can have different ploidy levels in different organs of the same individual.
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