Identification of the major groups within Platycheirus (males)

The taxonomy of Platycheirus on iNat has recently had a bit of a sort out. The result is the use of the generic/subgeneric framework established by Mengual (2020), and within that the Species groups suggested by Vockeroth and developed by Young, Marshall and Skevington. These Groups are called 'Sections' in iNat, because that is the rank that is available. Within the albimanus Section are the complexes scutatus and clypeatus. So it looks like this:

Genus Pyrophaena (aka granditarsis Group) Holarctic
Genus Eocheilosia New Zealand
Genus Platycheirus Holarctic,Neotropical
Subgenus Tuberculanostoma (formerly a distinct Genus) Neotropical
Subgenus Pachysphyria (aka ambiguus Group) Holarctic
Subgenus Carposcalis (aka stegnus Group) New World
Subgenus Platycheirus Holarctic
Section manicatus Holarctic
Section peltatus Holarctic
Section chilosia Holarctic
Section pictipes Nearctic
Section albimanus Holarctic
Complex clypeatus Holarctic
Complex scutatus Holarctic
Not in a complex Holarctic

(European identifiers in particular should note that the definition of 'Section albimanus' used here still conflicts with the definition sometimes used in Europe i.e. those species with white maculae - as it did before. White spots species are spread through the groups. In the UK for example 4 species are considered albimanus Group in this 'white spots' sense: ambiguus is in Subgenus Pachysphyria, discimanus is in Section manicatus, but the other two (albiimanus + sticticus) are in Section albimanus. This is why the concept cannot be implemented in iNat - the taxa have different parents.)

The morphological delineation of the groups within the genus Platycheirus goes primarily with the modifications of the male foreleg. Here is an attempt at a key to the groups on that basis, largely based on Skevington:

1. a. At least some segments of the male foreleg modified in shape.
b. Male foreleg modified only by the presence of ornamental setae, if at all.
2
4
2. a. Male foretibia unmodified in shape (only tarsi expanded).
b. Male foretibia modified in shape.
Section manicatus
3
3. a. Male foretibia broadening gradually throughout its length.
b. Male foretibia broadened distinctly at the apex only.
Section albimanus
Section peltatus
4. a. Face extended well forwards into a prominent pointed snout, but hardly downwards, and with a prominent tubercle, Males dichoptic.
b. Face not extended forwards into a snout. Males holoptic.
Subgenus Tuberculanostoma
5
5. a. Male forefemur with long curled bristle at the apex.
b. Male forefemur without such a bristle.
Subgenus Pachysphyria
6
6. a. Long curled setae on male forebasitarsi.
b. Without long curled setae on male forebasitarsi.
Section chilosia
7
7. a. Male foretibia without ornamental setae (i.e. leg unmodified).
b. Male foretibia with long posterior setae.
Section pictipes
Subgenus Carposcalis

Posted by matthewvosper matthewvosper, November 25, 2021 10:25 PM

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