Dubious Punctuation

Or, be careful with those Polygonia...

The butterflies in the genus Polygonia are characterized by a silvery/white mark in the centre of the ventral side of their hind wings.  These markings have earned them common names like "Question Mark" and "Comma". In the case of the Question Mark, the silvery mark is usually in two pieces - a hook and a dot, which superficially resembles the eponymous punctuation mark. In the various comma species, the two pieces are usually fused to form a "V" or "C" shape, sometimes with barbs at the ends.  Examples can be found on these pages:

The authors of some field guides use detailed descriptions of the shapes of these markings as field marks for distinguishing one species from another.  They do work as field marks most of the time, but what the field guides usually fail to mention is that there are exceptions to these "rules". Perhaps it goes without saying that no field mark works 100% of the time, but it is not unusual for some people to latch onto field marks and treat them as though they are not subject to variation. 

My own observation has been that these markings can be variable within a species. In particular, it appears that the markings are often not well formed on female Polygonia.  In addition, the ventral wing pattern of females is often different from that of males.  The colour is often more even, with less variegation.  Combined, this variability can trip up those who focus too much on the shape of the comma mark and/or the superficial appearance of the ventral hind wing colour/pattern. 

While looking at observations on reporting platforms like eButterfly, iNaturalist, and BugGuide, I have seen two categories of identification errors occurring with members of this genus: 

In the first case, the error occurs because the silvery mark on the ventral hind wing of a Comma is incomplete or "broken", making it look like the mark on the Question Mark.  Here is a typical example of a pale/winter form Question Mark: