Mapping UK Platycheirus recording groups onto iNat taxonomy

The Genus Platycheirus is a very large, nearly cosmopolitan genus of small elongate hoverflies typified by males with distinctive modifications to the shape and/or bristles of parts of the front leg. The fact that it is such a large genus means that it has been subdivided. Traditionally the subdivisions have been based on the morphology of these male forelegs.

In the UK, for the purposes of the National Hoverfly Recording Scheme, the genus has been split up into 'groups'. This is not a taxonomic statement, but one of convenience for recording by grouping similar looking species together. Of course it is often the case that 'looking similar' does have taxonomic significance, and most of the UK groups do indeed align with more widely used taxonomic units. The exception, as we shall see, is the albimanus-group.

The UK groups are:
albimanus-group: inc. albimanus, ambiguus, discimanus, sticticus
manicatus-group: inc. manicatus, tarsalis, melanopsis
peltatus-group: inc. peltatus, nielseni, amplus
scutatus-group: inc. scutatus, aurolateralis, splendidus
clypeatus-group: inc. clypeatus, angustatus, europaeus, fulviventris, immarginatus, occultus, perpallidus, podagratus, ramsarensis, scambus
(Note that Subgenus Pyrophaena i.e P. granditarsus + rosarum is considered a full genus in iNat, not part of Platycheirus at all)

Apart from the UK albimanus-group, all of the above mentioned groups have equivalents in iNat such that if you have a species identified as one of those UK groups it is fine to ID them as 'Section P peltatus', 'Section P manicatus', 'Complex P. clypeatus', or 'Complex P. scutatus' respectively.

The UK albimanus group however, which depends on the whitish or bronzish abdominal markings (as opposed to yellow in other species) could not be reconciled with a wider taxonomy from the literature. It is handy for recording convenience in the UK - but breaks down quickly under the weight of overseas species, and is not taxonomically meaningful anyway. 'Section P. albimanus' in iNat is a completely different concept. In fact 'Section P. albimanus' in iNat includes 'Complexes clypeatus and scutatus' (Which is why we had to use Sections and Complexes to implement these groups). In addition, two species of the UK albimanus group are not in 'Section P. albimanus' (P ambiguus and discimanus). Here is how it looks:

Genus Platycheirus
---Subgenus Pachysphyria (inc. ambiguus - this whole Subgenus is characterised by a curled apical bristle on the male forefemur)
---Subgenus Platycheirus (inc. everything except ambiguus)
------Section P peltatus (same as the UK group)
------Section P manicatus (=UK group + discimanus)
------Section P albimanus (=albimanus, sticticus and the two complexes mentioned below)
---------Complex P scutatus (same as UK group)
---------Complex P clypeatus (same as UK group)

Another way to look at this is:
If you know the UK group
you can give it the same ID on iNat unless there is a possibility that it is ambiguus or discimanus.
If you have an ID from iNat, the UK group will be the same unless the ID is albimanus-group and the spots are not grey, or the ID is manicatus-group and the spots are grey (but the latter case is unlikely to occur in practice).

I hope that makes some sense. I have intended to put out a key to help with this, but it will have to wait. Maybe not long...

Posted on 17 October, 2022 20:35 by matthewvosper matthewvosper


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