Phengaris is a genus of gossamer-winged butterflies in the subfamily Polyommatinae. Commonly, these butterflies are called large blues, which if referring to a particular species is P. arion, a species resident in Europe and some parts of Asia.

Phengaris is currently defined to include the genus Maculinea. The type species of the latter was the Alcon blue ("M." alcon). This species was found to be less closely related to most other supposed members of Maculinea than the traditional Phengaris species, and hence the two genera were merged to form a monophyletic group. Alternatively, Maculinea could be restricted to the one or two species of "Alcon" blues, and the rest of it be separated as a new genus. But this would create two very small genera, which is generally avoided by modern taxonomists. As Phengaris is the older name, it thus replaces Maculinea.

Maculinea was alternatively considered to be a subgenus of Glaucopsyche. But while Glaucopsyche and Phengaris (including Maculinea) are certainly close relatives, they are unlikely to be that close.

The most recently discovered species in the genus is P. xiushani, first reported in 2010 and found in undisturbed forested mountains, unlike all the other members which live in grasslands over their entire range of distribution.

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