the species group
Large genera can often become unwieldy, necessitating infrageneric ranks. In many cases authors wish to group similar species together for identification purposes, but do not want to give the group a formal name such as required for subgenera or sections. The species group fills this role, and has been used quite extensively in many speciose genera across disparate taxa. However, iNaturalist does not currently have a rank for this concept, and I thus propose that the taxon rank “species group” be added to the iNaturalist taxonomy. This feature request is born out of the discussion here: https://forum.inaturalist.org/t/large-genera-with-formal-species-groups/11073
The genus Efferia (Insecta: Diptera: Asilidae; https://www.inaturalist.org/taxa/61610-Efferia) is a large genus with nearly 200 known species and many undescribed. Hine (1919) proposed 8 species groups and these are frequently used by the community (e.g. https://bugguide.net/node/view/5188/tree). Efferia is the most observed genus of robber flies on iNaturalist (>8,000), and yet most observations are left at genus (~69%!) due to the large volume of similar species. However, using the species group rank (in the style of BugGuide) would allow for the more manageable sorting and identification of this genus. This principle applies equally well to many other genera that have existing named species groups.
An equivalent rank does not exist on iNat
There are currently five taxonomic ranks on iNaturalist between genus and species, and none of them are a proper substitute for species groups: genushybrid, subgenus, section, subsection, and complex. The first rank obviously is only relevant for hybridization events. Subgeneric names are governed by the codes of nomenclature, and while applying to similar concepts as “species-groups,” are not equivalent for this reason. Section and subsection are likewise formal taxa, although applying only to organisms covered by the ICBN (e.g. plants and fungi) and should not be used for animals. Finally there is the species complex, another informal rank that is best applied to closely related species that can be difficult to separate. Species groups are broader groupings of species and are not directly equivalent to the more narrow concept of complexes. Indeed, it is possible to have species complexes within species groups.
The terms formal and informal can have different meanings depending on context. Here I use the term “formal” to refer to ranks covered by codes of nomenclature such as the ICZN or ICBN, whereas “informal” ranks are not. While species groups are “informal” in this sense, they are often still rigorously defined in the literature.
implementation on iNaturalist
The rank of species group is perhaps best suited between subsection and complex. iNat staff evidently prefer ranks that consist of a single word without hyphens, so I propose “speciesgroup” or simply “group” for this rank. There has been discussion on how complexes are displayed on iNat (https://www.inaturalist.org/flags/331324), and while maybe not ideal, for the sake of standardization species groups can use a similar format: e.g. Group Efferia albibarbis. The curator guidelines for species groups would be essentially the same as for complexes (https://www.inaturalist.org/pages/curator+guide#complexes).