Hi Adriel,

Yes you can - some excellent discussion and definitons can be found in the following literature (I have used these often in my own taxonomic papers) - see below. These works define subspecies and forma very well and point out the ambiguity of variety - a rank I dislike because its definition is so labile and often clashes with subspecies.

Davis P.H., Heywood V.H. 1963. Principles of Angiosperm Taxonomy. Edinburgh & London, Oliver & Boyd, 556 pp.

Stace CA 1991. Plant taxonomy and biosystematics, 2nd edition. Cambridge University Press, Cambridge. 272 pp.

Stuessy TF 1990. Plant taxonomy. Columbia University Press, New York. 568 pp.

Other literature exists but these are good starting points.

Its also true that there seems to be no international consistency in the application of these ranks. For example in Aotearoa / New Zealand we use subspecies for allopatric segregation within a species yet others use it for variation within a sympatric / syntopic gene pool (see discussion on this problem in Davis & Heywood (1963)).

Hope that helps,

Cheers

Peter

Yes :)

Individuals of same varieties or forma produce, when crossed, an offspring as fertile as the parents (or more fertile than the parents in case of heterosis). Crosses between subspecies produce semi-sterile offspring.

At least for botany, it is common practise among taxonomists to use subspecies rank for allopatric variants and varietal rank for sympatric ones of the same morphological standing. However, as Peter James De Lange has already pointed out, there isn't really a standard that everyone follows.

For example, see Hamilton & Reichard, Taxon 41: 485-598 (1992). https://doi.org/10.2307/1222819

The best is to clearly state how you define them before using.

The forma is largely considered the least respectable category and many recommended against formally recognised it (which I also do). Regarded as having little to no value in taxonomy, recognising forma merely adds unnecessary complications to nomenclature.

I'm pretty much in line with preceding comments. In my taxonomic group (Hepialidae) varieties and forms were named entities mostly from the 1800's through to the early 1900's. Now no one does that anymore. Naming forms or varieties in a taxonomic context has no value. Subspecies as allopatric variants might be tried, but remains problematic. It sort of says that the populations are distinct, but not enough to warrant species status with current information. They might be 'species' or not. Anyway, best of luck with your efforts in your group.

I support the answers given independently by both John Grehan and Peter James De Lange and do what they do. I work with sea cucumbers and regard slight allopatric variations as subspecies and slight sympatric variations as varieties. In allopatric populations gross differences must be regarded as representing different species. I don't use the term forma (in fact never did). Don't be afraid to stick your neck out even if your think there will be repercussions.

I agree with the above answers. An additional aspect to keep in mind is that from a conservation perspective, anything below the species level is not recognized by the IUCN. So, since (in the case of botany) there is often no sharp boundary in terms of crossability, etc., it might be "better" to separate taxa at species level than below, if justified by the characteristics (molecular or morphological).

uo to your information.

Tilo thank you - the issue of conservation and how this applies to rank (and I guess the bug bear of 'Taxonomic Inflation') is addressed here if you are interested Article Trithuria brevistyla (Hydatellaceae), a new combination for ...

Obviously there will be other opinions on the matter.

As every taxonomist have expressed, there are as well different concepts on what is a species or infraspecific ranks are, also accordingly to the taxonomy followed on different groups the usage of these is heterogeneus, so from there you must decide or formulate what is or should represent a species, a variety or a subspecies philosophically speaking. However, if you need to prepare a diagnosis of what is or not and how, integrative biology is by far demostrating that most of what are called varieties or subspecies may fall in different lineages (different species) or just do not separate from the whole variation of a single taxon (same species), however, as you must decide other issues, e.g. the conservation ones (e.g. as suggested above for the IUCN) and when not complete evidence of genetical divergence exist, a philosophical document must be used as a reference for your evidence/results. A personal statement is that evolution is never complete, e.g. you may think that a taxon compared is now perhaps a single species, but at time, part of it may extingish or seggregate in different geographic lineages that may lead to speciation (e.g. varieties or formae that are evolving within a single population can colonize or reproduce in new physical spaces better than the typical because of better genetics), so it´s mostly a matter of space-time question. The following paper may help in something for take a decision on your question:

De Queiroz, K. 2020. An updated concept of subspecies resolves a dispute about the taxonomy of incompletely separated lineages. Herpetol Rev. 51(3):459–46 https://repository.si.edu/handle/10088/107184

Thank you all for your comments and participation. They are very interesting and helpful!

As previous commentators already mentioned, you can do this.

This problem is not new, and definitions of infraspecific taxa could vary to some degree depending on the species concept used.

Below are some additional works that aren't new but nevertheless I found them helpful in my work:

Christensen KI. 1987. Taxonomic revision of the Pinus mugo complex and P. rhaetica (P. mugo sylvestris) (Pinaceae). Nordic Journal of Botany 7: 383–408.

Cronquist A. 1988. The evolution and classification of flowering plants. 2nd edition. Bronx: New York Botanical Garden.

Hamilton CW, Reichard SH. 1992. Current practice in the use of subspecies, variety, and forma in the classification of wild plants. Taxon 41: 485–498

All the best.

@ Adriel I. Jocou,

Subspecies: This taxonomic rank lies in between the species and variety. A single subspecies may contain numerous varieties. It is a division of the species into subgroups because of the geographical isolations.

Variety: A group of plants, selected on the basis of similar desirable traits within the species will constitute a variety. These plants are very close in their genetic architecture. This taxonomic rank (variety) lies below the subspecies but above the forma.

Forma: A taxonomic rank lies below the variety. It is an uneven variant of a variety that can be distinguished by an individual or few linked genes. The variations present in the “forma” are minor and of little taxonomic importance.