example: genus chironomus, and subgenus chironomus
A subgenus is a rank in between genus and species, although it is not the only one and not every genus has subgenera (plural of subgenus). When a genus is split into multiple subgenera, one of the subgenera has the same name as the genus, so that’s why there is both a genus Chironomus and a subgenus Chironomus (Chironomus). This subgenus is known as the type subgenus.
See also this explanation:
https://forum.inaturalist.org/t/display-genus-along-with-subgenus-section-etc/14107/11
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as for where distinctions are made to define genera and subgenera, this is based on the consensus regarding generic delineations for a specific group. for example, a subgenus for a plant is unlikely to be an equivalent level to a subgenus of an insect.
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I can understand having a subgenus… but what I don’t get is why there is subgenus and section, and why some genera (e.g. Claytonia) skip directly to section and don’t have a subgenus. Seems like you’d have to have a subgenus before you would further divide into sections…
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Some of the subgenera in the squirrel genus Spermophilus were elevated to genus a few years ago to better define the differences in this group of mammals. Interestingly, some or all of those subgenera were genera in the past, then got lumped under Spermophilus, before they were split out again. Same for the subgenera in the bat genus Lasiurus. My impression is that subgenera in mammals either get mostly ignored or, following a phylogenetic study of the group, they end up elevated to full genera. The subgenus is a taxon that doesn’t get much respect.
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This has definitely been true for mollusks as well. I think part of the reason is to avoid the inherent trinomials of parenthetical subgenera.
The zoological and botanical naming codes are different. Section is really only a botanical term. Possibly fungi too can’t remember…
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No doubt. If the name has to be put inside of parentheses, I guess you might as well ignore it.
“What is the difference between a genus and a subgenus?”
Three letters. s u b
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same happens with arthropods (particularly hoppers). I think taking that extra step to look into monophyletic groupings within a genus is very useful as it helps with the division of over-stuffed genera. those groupings are often elevated to genus at some point (or are collapsed if they are not actually monophyletic).
The key point, which others have alluded to, is that taxonomic ranks are generally entirely arbitrary. If a taxonomist makes up a new rank and other people use it, it is just as valid as any other rank. If a taxonomist decided that what was a subspecies is actually a different family, and other taxonomists go along, well then you’ve got a new family. Other than species, where there are far too many definitions, none of these levels is defined in any way beyond being above and below each other. So the only definition of a subgenus is a taxonomic grouping just below a genus, and just above a section or species group or species. And the only definition of a genus is a taxonomic group just above those things and just below some other things. There is no biology to it, only linguistics and custom.
Section is a zoological term too btw, but of different rank.
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Subgenera are often used in large genera of insects where there are some well-defined groups, but also species that don’t clearly fit in one of them and so would not be able to be assigned a genus name if it were split up. Also, large genera are maintained when the whole thing is easily diagnosed but the constituent subgenera (representing clades) are defined by difficult characters such as male genitalia. Drosophila is an example of the former, and Hylaeus of the latter.
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