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Genus Plebejus

Melissa Blue - Plebejus melissa - male Butterfly - Plebejus saepiolus Karner Blue Butterfly  - Plebejus melissa Rocky Mountain Arctic Blue - Plebejus glandon Plebejus icarioides - male Blues - Plebejus icarioides Boisduval's Blue - Plebejus icarioides - male Plebejus
Show images of: caterpillars · adults · both
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Lepidoptera (Butterflies and Moths)
Superfamily Papilionoidea (Butterflies and Skippers)
Family Lycaenidae (Blues, Coppers, Hairstreaks, Harvesters)
Subfamily Polyommatinae (Blues)
Genus Plebejus
Synonyms and other taxonomic changes
Plebejus Kluk, 1780. Type species: Papilio argus Linnaeus
Rusticus Hübner [1806] [name rejected and invalid]. Type species: Papilio argus Linnaeus
Aricia Reichenbach, 1817. Type species: Papilio agestis Schiffermüller
Agriades Hübner, [1819]. Type species: Papilio glandon de Prunner
Lycaeides Hübner, [1819]. Type species: Papilio argyrognomon Bergsträsser
Lycoena Nicholl, 1901. Type species: Papilio argus Linnaeus
Albulina Tutt, 1909. Type species: Papilio pheretes Hübner
Latoriana Tutt, 1909 [name rejected and invalid]. Type species: Papilio glandon de Prunner
Vacciniina Tutt, 1909. Type species: Papilio optilete Knoch
Gynomorphia Verity, 1929 [name invalid when published]. Type species: Papilio agestis Schiffermüller
Eumedonia Forster, 1938. Type species: Papilio eumedon Esper
Plebulina Nabokov, 1944. Type species: Lycaena emigdionis F. Grinnell
Icaricia Nabokov, 1945. Type species: Lycaena icarioides Boisduval
Pseudoaricia Beuret, 1959. Type species: Polyommatus nicias Meigen
Ultraaricia Beuret, 1959. Type species: Lycaena anteros Freyer
Plebejides Sauter, 1968. Type species: Lycaena pylaon Fischer de Waldheim
Plebejidea Koçak, 1983. Type species: Lycaena loewii Zeller
Maurus Bálint, 1991. Type species: Lycaena vogelii Oberthür
Umpria Zhdanko, 1994. Type species: Lycaena chinensis Murray

An amazingly long list of synonyms that reflects the amount of attention that has been, and continues to be accorded the Blues.
Explanation of Names
Includes (as subgenera) Agriades, Icaricia, Lycaeides, Plebulina, Vacciniina, following the classification of Opler and Warren - and duplicated (with one exception; Icaricia) at All-Leps (see discussion in Taxonomy Forum)
Opler & Warren and BOA treat Plebejus podarce as a distinct species, whereas All-Leps treats it as a synonym of Plebejus glandon.
The old world genus Polyommatus (one introduced species in north America), would logically need to be included within Plebejus as well, if all the rest are, but this combination is not followed by any contemporary authors.

As currently recognized, the species included under each subgenus are as follows:
subgenus Agriades: P. glandon, P. podarce, P. optilete [P. optilete is often placed in a separate subgenus called either Albulina or Vacciniina.]
subgenus Icaricia: P. cotundra, P. icarioides, P. lupini, P. neurona, P. saepiolus, P. shasta
subgenus Plebulina: P. emigdionis [this subgenus is very close to Icaricia.]
subgenus Plebejus: P. anna, P. idas, P. fridayi, P. melissa, P. samuelis [American species are more often called subgenus Lycaeides, but are not separable from subgenus Plebejus.]
Note: As of October, 2013, the groups named Agriades, Icaria, and Plebulina, are listed under the separate family heading at BOA as separate genera, but not Lycaeides or Vacciniina. This change has not been made on the entire BOA website as yet, but will be encountered when referencing species there. It is not made at BugGuide yet.
Number of species included varies widely from author to author depending upon genus circumscription and upon interpretation of species limits. Within North America, when all segregate genera / subgenera are included, Butterflies of America currently lists 16, with the number climbing periodically as regional populations are afforded species status [i.e. P. lupinus, neurona, anna, podarce, cassiope, cotundra, samuelis, fridayi, etc.; it is notable and noticeable that most of these are Californian "species"]. The most conservative listings include only 9 or 10 species. Polyommatus icarus is not included in Plebejus by any North American author as yet.
Distinguished from other genera by usually showing all or most of the following traits:
eyes black when alive.
ventral wings with dark markings in disk of wing (postmedian row to base) usually all equally dark (most often black), and usually all or most rounded and not linear, nor are they fused into lines or bands across wings.
ventral wings with paired marginal and submarginal rows of dark spots (may be faint); inner row sometimes crescent-shaped, but not forming a zig-zag line; with none greatly enlarged into prominent dark eye spots (some on hind wing may be larger and a little more prominent than others, but not greatly so).
ventral hind wing with marginal dark spots containing metalic bluish or greenish scales (may not show on old faded specimens, but usually at least some remain).
note: In some species, most or all dark markings may be prominently ringed in white, and the white may replace most or all of the dark color, but the markings are still present in the same arrangement and basic shapes.
hind wing (and sometimes front wing) may have orange submarginal markings between marginal and submarginal dark spots (sometimes showing above as well).
fringes of wings white, not checkered (without prominent dark coloring at vein tips).
no tails on hind wings.

These traits will not distinguish Polyommatus, but the single introduced species is distinctive and easily recognized.

A large and varied group, and several species can be confusingly similar. However, species mostly aren't too difficult to identify with close attention to both the under side (best) and upper side (helpful too). Pay attention to how many spots are in the discal cell of the front wing below. Are the spots below ringed in white, or are there large whitish patches? How are the spots arranged in relation to one another, and what shape are they? Look for orange pigment both above and below, and if there is any on the front wings. Is there a dark spot in the middle of the upper side of the wings? What is the habitat like (is it in a moist spot in the desert, or above timberline in alpine tundra, or . . . . )? The shape of the wings can help too (Is the outer margin straight? Is the tip of the front wing pointed?). A look at the thumbnails on Butterflies of America can be a useful aide as well.
Northern Hemisphere. Many species occur in both Eurasia and in North America. Some apparently range across both continents (though authors disagree and debate species limits, and whether or not Eurasian and North American insects are really the same or different species).
Internet References
Agriades, Albulina, Aricia, Plebejus, and Polyommatus at Markku Savela's website