It's not impossible that the picture shows
escheri (I agree,
thersites is ruled out by the submarginal markings, despite it sitting on sainfoin), but what caught my eye especially, zooming in on my iPhone, was the evident cell spot. I think we've discussed before the possibility of a cell spot very occasionally in
escheri but it must be the exception rather than the rule and so
prima facie evidence against that species. I would have called it
icarus. The half-chequering is not too much for that species.
To get back to Paul's original question, Roger's amazing PCHB illustrates how many of these superficial features, like silver spots, that we might associate with a particular genus, are not so deeply engrained in its identity as we might think! Many of them can appear sporadically in other genera. To my eye, the predominant characteristic of underside
Plebejus is the lack of the white paint stroke in ss.4-5. Instead, the white surrounding the submarginal lunules forms an even band, or is more or less evenly moulded to the lunules. In
Lysandra,
Polyommatus,
Aricia and other polyommatine groups the white paint stroke stands out a mile.
HOWEVER, when it comes to the origins of species, biochemistry trumps morphology every time (in terms of evidential value)!! The fact that all our European
Maculinea, which are morphologically so similar, are now classed in two different branches of
Phengaris, with
alcon and
arion widely separated from each other (more closely related to butterflies that look quite different than to each other) shows how misleading appearances can be (see:
http://tolweb.org/Phengaris/112250). Morphology can converge well after species separate (or diverge very rapidly if one evolutionary branch continues in a different environment) and features can be repressed or remain hidden from the outside when the potential to make them is clearly there in the genes. Although in principle biochemistry could converge it is far less likely to than morphology, and none of it is hidden.
Those are my thoughts, anyway. Silver scales very interesting, but probably not indicative of a closer relationship than previously imagined.
Guy