It is my understanding that variety is being faded out, at least for animals, why is this? Is the taxonomic rank variety still valid? Do taxonomists still describe varieties?
My understanding (at least for mollusks) is that varieties usually donāt represent clades and thus arenāt used to describe taxa. Often they are color, size, or range variants, or something like that. However, many species were originally described as variants of other species, and later study showed them to be distinct. Nowadays, people donāt describe variants, though, because they arenāt defined as representing clades. They may get a passing mention, but I wouldnāt really consider it a ātrueā taxonomic rank. But thatās just my impression. Itās probably different for plants, and I havenāt looked to see what the ICZN says.
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Please keep in mind that plants and animals have different codes of nomenclature.
Certainly in plants the rank of variety is not being phased out and is in fact the main traditional rank employed.
Also worth mentioning that the taxonomic rank of āvarietyā is not the same as a variant. It has a clear and precisely defined meaning in the respective codes of nomenclature.
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Exactly, in ICZN the lowest category is subspecies.
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In botany, you can think of a variety as speciation in action. A widespread species occurs in different climate conditions across its range, and natural selection is favoring slightly different traits in different parts of the range, to the point that we can distinguish a few traits that are visibly different when we compare those distant populations. Traditionally, ranks went species, subspecies, variety, form.
The problem is, some botanists were splitters, and named every minor variation that they could see within a species, whether it had a geographical component or not. Other botanists only used subspecies when naming populations, but some only used varieties, and others used both. Though the subspecies then variety idea was a good one, no one applied it uniformly, plus we start to get down to such minor genetic differences that it gets very hard to decide if your plant actually fits in a particular subgroup.
These days, for the sake of uniformity, I seem to see most botanists using subspecies and not bothering with varieties. I admit, many times, I often only ID a plant down to species, because I donāt feel like I can reliably ID to variety or subspecies.
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As @thomaseverest says, it works that way for moths as well. Some moths have distinct varieties that may or may not be geographic in nature. They are the same species, though. Some people put a comment on their observations, something like ādark variantā, but it is not a taxonomic distinction.
Then we also have different species of moths that look basically identical when individual variation is factored in! Why canāt life just be simple 
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Speciation processes in plants do not necessarily involve a geographic component. Distinct lineages often develop sympatrically due to drift in traits related to reproduction, polyploidy events, and specialization to localized substrates or habitats within a shared range. Naming of subspecies and varieties in plants should not be expected to be less valid just because the named taxa share a range with other subspecies or varieties. With modern techniques itās even coming to light that cryptic species with overlapping ranges and nearly identical morphologies exist despite being entirely distinct evolutionary lineages. How to handle such cases is not without controversy. It is interesting to note, though, that many āsplitsā in the past that had more recently been lumped are being shown to be validly distinct lineages through genetic analysis (though certainly not all), so itās not particularly fair to call past botanists inclined to be āsplittersā a problem.
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Not only that, but in botany we have subspecies that are split into varieties, which can themselves be split into forms. The ranks are hierarchical. However the valid trinomial according to ICN includes only the lowest level rank named.
For example, the valid trinomial for Bedfordia linearis subsp. oblongifolia var. curvifolia is Bedfordia linearis var. curvifolia.
Traditionally, in botany, only subspecies have been used to denote variation with a substantial biogeographic component, whereas varieties may or may not have had overlapping distributions.
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Yes, in animals, variety is not a taxon. At least in vertebrate animals, subspecies (the lowest rank) seems to be fading in use but itās not close to gone. I havenāt seen a description of a new subspecies in herps or mammals for a long time. For many taxa, molecular studies have resulted in quite a few subspecies being elevated to monotypic species. Others have been dropped based on recent evidence they arenāt distinct. The result is an increase in monotypic species in many groups and a decline in recognized subspecies.
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Thank you all for your replies! Somewhat of a related question, is it worth spending the time identify plants to variety or is this unnecessary?
If those varieties are in taxonomy of website and you can id them, ofc it does worth it! Especially if you start with those that are still in needs of id. Thereāre also oftenly used varieties of animals, like feral pigeons, that are highly valuable to add.
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Lots of botanists still actively use variety, usually instead of subspecies. There is considerable discussion in the literature about how var. and ssp. have become essentially interchangeable in how they are applied in botany. Very few recent publications use both catagories. This differences seems to me to reflect differing concepts of taxonomy, with one tendency using just subspecies as major variations within a broadly drawn species, while the other tendency would assign at least some of those āsubspeciesā to full species status and assign less major but still recognizable and reasonably consistent forms to varieties, often with but not necessarily requiring a geographical component. And, certainly, there are many instances of subspecies in the literature that have broadly overlapping rangesā¦
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Itās definitely worth IDing to variety if you can confidently do so. If something is ambiguous, then only go as far as you are confident. Some varieties have been and will again be recognized as species. Some species will be reduced to varieties at some point. There is no consistency in how people distinguish species, subspecies, varieties, forms, etc., and there probably never will be. For the taxonomic work Iām doing on a plant genus, Iām going to use varieties and not subspecies as that is what is commonly used in the genus Iām studying. These varieties are all geographically distinct as are probably most varieties. I have already raised some varieties to the species rank and will recognize some previous species as varieties. I donāt know why animal taxonomists started using subspecies instead of varieties but that is least part of what has led to confusion in plants where mostly European and Californian botanists have followed the trends of animal taxonomy. Reading various papers about it, it goes back to at least Darwin as he was inconsistent in what he did. Inconsistency is apparently a long-standing tradition in taxonomy.
Please identify to variety or subspecies when possible. (Sometimes itās not possible.) Sometimes it really does matter. Consider the rush Juncus effusus. Three subspecies, all present in the Pacific Northwest, only one native. I think it matters whether the ones present are native or not.
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It seems to be not so trendy among botanists but it could turn out to be useful when two very close taxa (not enough distinct to be species) do not match the requirement of geographical or ecological vicariancy.
EDIT: among SOME botanists
Varieties are very much trendy among the botanists I hang out with. But theyāre admittedly mostly taxonomists.
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