Rebeli is very closely related to, and now considered a subspecies of, the Alcon Blue (P. alcon), and the differences (such as they are) are described on the alcon page.

Apart from possible confusion between rebeli and alcon (which I believe do not fly together), it is a large butterfly and could only otherwise be mistaken for the Large Blue (P. arion), which also flies at high altitudes and often in company with rebeli, although the male rebeli upperside is blue with clear black borders, lacking the black upf "splashes" of arion.

The female is largely brown-black with a varying amount of blue in the basal regions and a series of post-discal black "splashes" (common to Phengaris species) often merging into the dark borders.

The underside ground colour does seem to be different between the sexes, although not indicated in T&L; the males seem to me to have a bluish colouring and slight basal blue flush, whereas the females have a distinctive brown colouring.

The female seems to spend all of its time seeking out the larval hostplant Cross Gentian (Gentiana cruciata) and egg-laying on it. If you see a female in flight it is very likely to lead you to G. cruciata which often have a number of white rebeli ova visible in the newer shoots.

In the new European taxonomy, this species is now considered to the higher altitude subspecies of alcon and no longer a separate species. This species was previously known as Maculinea rebeli.

observations

a male, with the clear mid-blue colouring and distinct black borders, albeit slightly faded.

a male, slightly fresher than 12120 and a brighter blue.

a female upperside which matches the illustration in T&L quite well. It is very similar to the high altitude form of arion, and arion was present at this site, but I had seen the underside clearly so can be fairly sure it was rebeli.

a male, rather darker and with a basal blue flush.

a female egg-laying on G. cruciata. One egg is visible in this shot.