Taxacom: Collective groups and form(al) genera

[Francisco Welter-Schultes]

Dear Mario,
If author A established a new species and a new genus, say Aus bus, that 
nominal genus Aus is regularly established, and the newly discovered 
species Aus bus is its type species.

 From a nomenclatural point of view, authors B and C do not "add" new 
species to the same genus, but just place the new fossils in that same 
genus. The genus does not experience any modification just because 
authors B and C consider the new fossils to belong to it.
Authors B and C are free to place their new species in that genus 
without any reasoning. Authors in many animal groups usually do that if 
they do not like to establish a new genus. Some authors use a question 
mark behind the genus to indicate their doubts (Aus? cus n. sp.), others 
express it verbally. The Code allows this and has Art. 11.9.3.4. for 
such situations:
"the generic combination, although it must be unambiguous, can be 
tentative;"

If authors D and E apply the name of that genus Aus to a collective 
group, calling it a form genus and considering that the assemblage of 
species cannot be placed with certainty in known genera, and if they do 
not consider Aus as a known genus in that sense, they use this name for 
a collective group. As long as they do that, Art. 67.14 applies, the 
type species is disregarded, the name can be used for a collective group.
Other species can be added to this collective group, even if they were 
established earlier and even if they are type species of genera that 
were established earlier than Aus, and the community can continue to use 
the name Aus for the collective group.

If another author would not follow their view, and would regard Aus as a 
known genus, that author can use Aus as a regularly established genus by 
Author A, with its type species Aus bus.

It depends on the individual publication. For those who regard Aus as a 
collective group, Aus bus is disregarded as its type species, and for 
those who regard Aus as a known genus, Aus bus is its type species.

The term "known genus" is a taxonomic expression. It should mean that it 
can be placed somewhere in the system, taxonomically delimitated against 
other genera. An author who considers this as impossible, and who judges 
that this genus with its type species could be placed at many different 
locations in the system, and that the species could belong to any one of 
various genera, would prefer to regard it as a collective group, which 
allows to cover a wide range of taxonomic placements for the species in 
question.

Maybe we can use a very simple example. Author A discovers a fossilized 
leg of an ant with very special characteristics, clearly a new species, 
but unclear to which genus it belongs. The author describes Aus bus n. 
gen. n. sp., stating that the placement of Aus inside the ant taxonomy 
is uncertain. Aus is not the name of a collective group because Aus bus 
is one single species, not an assemblage of species.

Other authors discover fossilized legs of more or less the same kind, 
but different at species level, and assign the new fossils to the same 
generic name, Aus cus and Aus dus, and regard Aus as a collective group 
because any of the three species could be placed at very much different 
locations in the ant system, remotely from each other.

Suddenly someone discovers an entirely preserved ant body having the 
same legs as Aus bus, and so Aus bus can be placed with certainty inside 
the ant system.

 From this moment onwards Aus would be regarded as a known genus, and 
the name for the collective group in which Aus cus and Aus dus would be 
placed would have to change. Authors could use the next name they like 
for that collective group, if one is at hand, or establish a new 
collective group name for the assemblage of the two species.

This is how I understand it. If this answers your questions.

Best wishes
Francisco

Am 25.06.2025 um 17:56 schrieb Mario Sch?del via Taxacom:
> Dear Francisco,
> 
> could you explain in a bit more detail what it means to not be able to 
> "allocated with confidence to nominal genera". When dealing with 
> fossils, especially those of arthropods, the story usually goes like 
> this: Author A describes a species, the type specimens clearly do not 
> belong to any previously described species. At this point, everything is 
> still unproblematic. Then, other authors B and C add new fossils as new 
> species to the same genus, usually without any proper reasoning and 
> purely based on superficial resemblance and absence of differing 
> features that are visible in the fossil. These authors usually not state 
> that the genus will become a form genus or a collective group by 
> including their new species. Only later, other authors D and E then call 
> it a form genus. Does this genus name then qualify to be a collective 
> group, even if the situation when the first species was described was 
> unproblematic (monotypic genus)? My confusion probably relates to the 
> term "nominal genus".
> 
> Thank you very much in advance!
> 
> Mario
> 
> 
> On 6/25/25 17:12, Francisco Welter-Schultes via Taxacom wrote:
>> Dear Ziv,
>> If you propose a name for a collective group, that name would 
>> automatically not have a type species no matter if you designate one 
>> or not. You could not fix a type species for it, any type species 
>> designation would be invalid. You could designate one, but only 
>> ineffectively.
>>
>> For the collective group see the definition in the Glossary:
>>
>> "collective group. An assemblage of species, or stages of organisms 
>> (e.g. eggs or larvae), that cannot be allocated with confidence to 
>> nominal genera. Names proposed or used for collective groups are 
>> treated as genus-group names but special provisions apply to them (see 
>> Article 42.2.1)."
>>
>> If you propose a name for an assemblage of species which you cannot 
>> allocate with confidence to nominal genera, you propose a name for a 
>> collective group. Once this condition is met, "assemblage of species 
>> which you cannot allocate", the rest follows automatically. As said 
>> above, even if you designate a type species this act will be 
>> ineffective and invalid. It would not render your name anything else 
>> but a name for a collective group.
>>
>> If the form genera you are talking of were proposed for such 
>> assemblages, which the authors demonstrably could not allocate with 
>> confidence to nominal genera, they fall under the definition of a 
>> collective group. Consequently these names do not have type species - 
>> and any type species designation would be invalid.
>>
>> It is not possible to state "the form genera have type species, so 
>> they are not collective groups". The condition of the Glossary 
>> definition is superior. If they are collective groups because they 
>> comply with the Glossary definition, they have no type species, and 
>> any previously published type species designation is to be rejected as 
>> invalid.
>>
>> This is how I understand the Code in this matter.
>>
>> I hope this helps.
>>
>> Best wishes
>> Francisco
>>
>> Am 25.06.2025 um 04:50 schrieb Ziv Lieberman via Taxacom:
>>> Hi all,
>>> I'm thinking about the differences between "form" or "formal genera" and
>>> "collective groups" and how to best approach these entities when
>>> establishing new nomenclature.
>>> In ants, there are many groups of fossil taxa which have been 
>>> established
>>> for convenience, without implying that they form a natural group - 
>>> mostly,
>>> e.g., impressions of wings or incompletely preserved fossils which 
>>> can be
>>> associated based on one or more morphological features. Authors 
>>> generally
>>> state that these are "form genera" (or, perhaps confusingly, "formal
>>> genera", especially in the Russian school of paleontology). However, 
>>> they
>>> are nomenclaturally treated as "real" genera, including in that they 
>>> have
>>> type species.
>>> To my understanding, these "form genera" align with the Code's 
>>> definition
>>> of collective groups: "An assemblage of species. . .that cannot be
>>> allocated with confidence to nominal genera. Names proposed or used for
>>> collective groups are treated as genus-group names but special 
>>> provisions
>>> apply to them". These provisions are given in 42.2.1 ("The names
>>> established expressly for certain assemblages of taxonomic convenience
>>> known as "collective" groups. . .established at the genus-group level 
>>> are
>>> to be treated as genus-group names in the meaning of the Code." 42.3.1
>>> states "Collective groups have no type species."
>>> Therefore, I arrive at the conclusion that even though many "form(al)
>>> genera" are "established expressly for assemblages of taxonomic
>>> convenience", they are *not* collective groups, since they have type
>>> species.
>>> This leads to my direct question: If I want to establish a new 
>>> collective
>>> group, should I follow 42.3.1 and not fix the name to a type species? 
>>> This
>>> seems like it must be the right answer, but I am hesitant because I have
>>> never seen an example of such a name in practice.
>>> Further, if the type species of a form genus is transferred to a 
>>> type-free
>>> collective group, are there any additional complications to consider?
>>> Thank you!
>>> -Ziv
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