Pyrgus key - underside view

This is attempt at an identification key for Pyrgus species based on the underside view.

A key based on the upperside view is here.

note: these observations will hold true for about 98% of specimens, but natural variation will produce some that do not fit the "classical" template.

note: location, flight period, altitude have not been included in the criteria.

The main underside hindwing markings are circled above.

Externally = toward the margin. Internally = toward the base of the wing.

 

Start here:

It is suggested that each step is taken in the order shown, to eliminate those species  with a unique defining characteristic.

Size (small/medium/large) is given as an additional indicator, although size is relative and can vary; as a baseline, P. malvae (or malvoides) is small.

step characteristic size yes no
1

Border of margin clearly white or distinctly pale for the entirety of the margin, and of broadly constant width (except for the marginal markings). The very edge of the margin is pencil-thin and darker

 large Pyrgus carthami 3.1
2 The two bands between the three white basal/discal/marginal bands are bright or pale yellow large Pyrgus sidae 3.1
         
3.1 Discal s4/5 broadly symmetrical and anvil-shaped, usually black-edged for all or part of this mark medium 3.2 3.3
3.2 Discal s1 non-regular, split in the centre to some degree with the top half noticeably displaced internally, and the mark generally strongly leaning internally   Pyrgus onopordi 4.7
3.3 Discal s4/5 narrow and deeply cleft externally small 3.4 4.1
3.4 Markings generally small and discrete   3.5 4.1
3.5 Veins prominent   Pyrgus malvae 4.1
3.6 Discal s4/5 regular rectangular, straight-edged, aligned with discal s6/7 small 3.7 4.1
3.7 Basal s7 broadly rectangular   Pyrgus warrenensis 4.1
         
4.1 Basal s7 broadly round or oval, or the sides are significantly curved where they meet the veins to form a semi-round shape medium 4.2 5.1
4.2 Marginal s2 broadly pointed arc-shaped and filled solid   4.3 4.7
4.3 Discal s4/5 quite wide (width about 1.3-1.5 times the height), internal edge almost straight, external edge not strongly cleft   4.4 4.5
4.4 Discal s1 broadly symmetrical and non-leaning   Pyrgus serratulae 7
         
4.5 Discal s2 empty or very small medium 4.6 6
4.6 Marginal v5 rectangular (width about 1.3-1.5 times the height) and with a reasonably neat internal edge   Pyrgus carlinae 5.1
4.7 Marginal v5 square-ish, amorphous internal edge and washed over reddish   4.8 5.1
4.8 Discal s1 banana-shaped and strongly leaning internally   Pyrgus cirsii 5.1
         
5.1 Discal s1 thin medium/large 5.2 6
5.2 Ground colour grey to grey-brown   Pyrgus cacaliae 5.3
5.3 Discal s1 more of a white streak, pointed at the external end   Pyrgus andromedae 6
         
6 Discal s1 broadly regular and slightly leaning internally medium/large 6.1 7
6.1 Ground colour dark brown   6.2 7
6.2 Veins prominent   6.3 6.5
6.3 Marginal s2 sagittate, broadly regular and non-filled   6.4 7
6.4 Discal s2 present   Pyrgus armoricanus 7
6.5 Marginal v5 short and with an irregular internal edge   6.6 7
6.6 Marginal s2 amorphous   Pyrgus alveus 7
         
7 Discal s1 exceptionally large.   Pyrgus foulquieri