Butterfly systematics

• Genera
• Species
• Subspecies

All plants and animals in the world, whether living or fossil, are classified in a system of scientific names that is accepted universally and is regulated by an international code of nomenclature (the science of naming organisms). The most basic system of classification is called binomial nomenclature, whereby every plant and animal is identified by a unique two-part name consisting of a genus name and a species name. This system, developed by the Swedish botanist Carl von Linné (Linnaeus), was first applied to butterflies in 1758. All butterflies, including skippers, were placed by Linnaeus in a single genus (Papilio) and given species names in this genus (e.g., Papilio antiopa Linnaeus is the Mourning Cloak).

Since the time of Linnaeus, butterflies have been arranged into many hundreds of genera (plural of genus) to better show their relationships: the Mourning Cloak is now known as Nymphalis antiopa (Linnaeus). These butterfly genera, like those of all plants and animals, are arranged into a hierarchical classification that classifies plants and animals into superfamilies, families, subfamilies, tribes, genera, species, and subspecies. Most of these categories are subjective, and different specialists may disagree on how inclusive or restrictive they should be. For example, the differences between the former butterfly families Satyridae, Nymphalidae, Danaidae, Heliconiidae, and Libytheidae are now recognized by most researchers as being relatively trivial when compared to the differences between other families of butterflies, so the recent trend is to treat each of these groups as a subfamily within the family Nymphalidae.

The scientific name of each species is followed by the name of the person who proposed the name, and the author's name is given in parentheses if the name was proposed in a different genus than the one now used. For example, Nymphalis antiopa (Linnaeus, 1758) was proposed by Linnaeus in 1758, but in a genus other than Nymphalis; in this instance, it was in the genus Papilio. Where the date of a publication in which a name was first proposed is actually different from the date printed in the publication, the corrected date is shown in square brackets; there are many examples of this in older butterfly names.

There has been general agreement among systematists (scientists who study evolution and classification) that butterflies should be grouped into two superfamilies: Hesperioidea for skippers and Papilionoidea for the "true butterflies." Also most of our butterfly species are well defined and firmly established through years of research and debate. In some instances, however, several "species" may still be combined into a single species, or species "split" into additional species as further research adds to our understanding of butterflies. More rarely, species new to science are still being discovered and described. Most of the controversy that persists in butterfly classification is in arranging geographical variation in butterflies into "subspecies" and in defining the limits of some genera and species. Some difficulties with genera, species, and subspecies are discussed in detail below.

GENERA

A generic name is used to associate a group of closely related species. Since the limits of a genus are subjective, there has been disagreement among specialists as to whether some groups of butterflies should be placed in a single genus or arranged in a larger number of smaller genera. There was a tendency in the 1960s and 1970s to subdivide genera into smaller genera that were frequently defined on relatively trivial characteristics. The need for many small genera can be alleviated by using the categories of subgenera and species groups; these two categories are most frequently used by the specialist to develop a classification that gives a higher resolution to details of how the species are related without having genera that can only be recognized by the specialist.

Through many years of research and debate, the limits of most genera have been established and accepted by butterfly researchers, and many small "genera" were eliminated in the 1980s as a more conservative approach to generic classification became established. Twelve generic names still remain controversial in that they continue to be "split" or "lumped" by different workers. Unfortunately this is usually done without explanation, so we have included below a brief discussion of these twelve genus-group names to explain our usage of them. They are discussed in the order in which they appear in the text. Our usage and a comparison with several frequently used reference works are summarized in the table below.

Papilio
There has been a tendency to subdivide swallowtails into smaller genera to reflect groupings based on wing pattern, larval appearance, and so on, so that the tiger swallowtail group was placed in the genus Pterourus, the giant swallowtail group in the genus Heraclides, and the black swallowtail group in the genus Papilio. Miller reviewed this situation in his comprehensive revision of the higher classification of the swallowtails of the world and concluded: "Recent attempts to subdivide Papilio into genera... are unconvincing" (Miller, 1987: 386). We follow Miller in accepting a more inclusive concept for the genus Papilio and treat these smaller groupings as species groups within Papilio.

Pieris
Some authors place the genus Pontia within Pieris, but a review of Pieris classification by Robbins and Henson (1986) demonstrated the generic distinctness of the two genera and showed that Pontia is not as closely related to Pieris as are several other pierid genera.

Colias
Some authors place the Southern Dogface (Zerene cesonia) and its relatives in California and South America within the genus Colias. Zerene differs in numerous characters of the genitalia from Colias and has a more primitive wing venation that resembles other Coliadines (Klots, 1933: 175-6). Colias contains about 50 species in the world, and with Zerene excluded Colias is structurally a homogeneous genus.

Lycaena
A detailed revision of Lycaena of North America by Miller and Brown (1979) resulted in the 18 North American species (12 in Canada) being placed in seven genera, with small differences in wing venation, leg spining, and genitalia being used to group the species into the smaller genera. These genera are so narrowly defined around a single species (the type species) that other species placed in the genera fit poorly. For example, three of the genera contain a single species, "Lycaena" cupreus is only tentatively placed in Lycaena, and "Gaeides" gorgon is stated to be in between Gaeides and Chalceria. While these studies serve to illuminate the relationships among species of coppers, we believe that such fine partitioning of Lycaena is best dealt with by using subgenera and species groups, categories ideal for detailed classifications used by specialists. An example of further complications with such finely divided genera is discussed by Pratt et al. (1991: 177). The coppers of Europe are placed in four genera, one of which is Lycaena (Higgins, 1975). These four genera are structurally much more divergent than are our coppers; the North American coppers all fall within the limits of Lycaena in Europe.

Satyrium
The Coral Hairstreak (Satyrium titus) has been placed in its own genus (Harkenclenus) by many authors, because in the male genitalia the aedeagus (penis) has only a single sclerotized apical rod in the membrane compared to two apical rods in Satyrium. In all other features the Coral Hairstreak is the same as Satyrium (some western Satyrium also lack tails). In an evolutionary context, however, the single rod does not tell us anything about the relationships of titus; we know that it has lost one rod (since other relatives of Satyrium also have two rods), so titus might be a relative of any of the species in Satyrium. We also know that titus has an enlarged, rounded sclerotized lobe on each side of the genitalia (projecting from the tegumen), a condition not found in most Satyrium or in related genera. An identical lobe is present in the acadicum group of Satyrium. Thus, the evidence points to titus being most closely related to the acadicum group but differing in its loss of one rod (it is actually present but lightly sclerotized and difficult to see). To place titus in its own genus obscures its natural relationship next to the acadicum group. Thus, we have included titus in Satyrium.

Callophrys
This genus was divided into six subgenera by Clench in Ehrlich and Ehrlich (1961). Although the structural differences among these subgenera are slight, compared to those among other thecline genera, Miller and Brown (1981) listed them as full genera and authors have been divided on the status of these "genera/subgenera" ever since. The tenuous nature of the characters separating these "genera" were illustrated by Warren and Robbins (1993) in their report of a hybrid between "Incisalia" augustinus and "Callophrys" sheridanii. In particular, the valve "cap" (a sclerotized thickened area at the apex of the male valve), used to characterize Incisalia, is shown to be present also in Mitoura and Callophrys, but expressed to a lesser degree. As a result, we treat Incisalia and Mitoura as subgenera of Callophrys.

Plebejus
The Plebejus group of genera includes five genera in Canada, with one other genus in the United States and another twelve in Europe. The five genera in Canada fall into two groups, with Plebejus, Lycaeides, and Icaricia being closely related and Agriades and Vacciniina forming the second group. Some authors (e.g., Scott, 1986) lump all of these genera under Plebejus; others (e.g., Ehrlich and Ehrlich, 1961) maintain Agriades while lumping the other four under Plebejus; Opler and Malikul (1992) lump Icaricia with Plebejus but keep the others separate. We have dissected material of these genera and compared this with European material and with the generic diagnoses given by Higgins (1975). We maintain all five genus names for the Canadian fauna. Icaricia differs from Plebejus in male genitalia structure: a long tapering penis; broad, medially expanded labides; and short, vestigial falces. In fact, we would have been tempted to lump Icaricia with the European genus Aricia Reichenbach, which is structurally identical to Icaricia, were it not for the different habitus of the adults of the two genera. We leave a technical study of these genera to a more appropriate scientific revision.

Boloria
This genus has two somewhat divergent species in Canada, eunomia and napaea. In the male genitalia both lack the upturned process at the apex of the valve. There is a process from the dorsal margin of the valve that is finger-like in most Boloria species, but in these two species there is a dorsal lobe on the process (apical in eunomia making the process appear bilobed, mesial in napaea making it appear triangular). Because of these differences, these two species were placed in their own genera as Proclossiana eunomia and Boloria napaea (with its Old World relatives), with all other North American species being transferred to Clossiana. Grey (1989), the leading authority on this group, concluded that there is little justification for recognizing Proclossiana, but that Boloria, in addition to the characters given above, is divergent in having a heavily spiculate dorsal process in the genitalia (the uncus). He reluctantly concluded that Boloria and Clossiana should remain separate, but "[t]his, however, is only because Miller & Brown [in their check list] do not use subgenera" (Grey, 1989: 2). Troubridge and Wood (1990) suggested that Boloria in the broader sense is a well-defined and well-known group and the slight differences exhibited by eunomia and napaea do not justify dividing the genus. We agree with their conclusions.

Chlosyne
This genus has been split by some authors into two genera: Chlosyne and Charidryas. Higgins (1960) prepared a world revision of the Chlosyne group and arranged the species in nine genera. He arranged the species in the restricted genus Chlosyne into three species groups with the statement: "Although these three groups are obviously distinct by distribution and in external features, they appear to be so closely related by every criterion of stucture that I have not been able to find any character that would justify generic separation" (p. 395). In Howe (1975) Bauer placed the two northern groups, which include all seven species in Canada, in subgenus Charidryas and the more southern group, which includes many mimetic forms, in subgenus Chlosyne. Charidryas was raised to the status of a genus by Ferris and Fischer (1977) on the basis of wing pattern and distribution differences. Higgins is known to prefer to split genera whenever possible, so his statement indicates the lack of justification for this split. A number of groups have more mimetic forms in the south; this is evident even within a species (e.g., White Admiral versus Red-spotted Purple); therefore we place the Canadian species of this group in Chlosyne.

Limenitis
The White Admiral group in North America is sometimes placed in a separate genus (Basilarchia) from Limenitis of Europe. There are no significant structural differences in adults or larvae between Limenitis and Basilarchia and we treat the two as a single genus. Ladoga is a closely related Eurasian genus that has until recently been combined with Limenitis. It includes camilla (Linnaeus) and two related species. Ladoga is similar to Limenitis in genitalia structure, but the eyes are hairy and the larva is very different from that of Limenitis, with paired branching spines along the back; Limenitis larvae have a pair of large spiny clubs on the thorax and several areas of spiny warts along the back.

Lethe
The genus Lethe is a large Southeast Asian group of satyrs that superficially resemble Enodia and has been used by some workers for species placed in the genera Enodia and Satyrodes.

SPECIES

Species are defined as individual organisms and populations of organisms potentially capable of interbreeding. Most butterfly species in Canada are well defined and easily identified. In some instances, however, the limits and identity of species can be confusing. For example, the Spring Azure (Celastrina argiolus (Linnaeus)) and the Mustard White (Pieris napi (Linnaeus)) have both been treated for many years as single species that occur throughout most of Eurasia and North America. Recent research has shown that both are species complexes with several species involved; the number of species, their defining characteristics, and their geographical ranges are still imperfectly known.

Similar confusion exists in other groups, especially among some blues, sulphurs, marbles, and swallowtails. In other instances, populations that are currently treated as geographical subspecies of a single species may in fact be distinct species, with supposed zones of hybridization actually being variation that superficially looks like hybridization. Some of the greater fritillaries (Speyeria) are examples of this phenomenon.

A third type of problem in defining species is seen in groups such as fritillaries (Boloria and Speyeria), sulphurs (Colias), blues (Euphilotes), and hairstreaks (Callophrys subgenus Mitoura). In these groups different populations may come together in some areas and behave as distinct species with little if any hybridization, while in other areas their ranges come together and they interbreed freely. These populations fall in between the species and subspecies categories and our treatment of them varies with the individual circumstances. For example, we treat Callophrys rosneri and C. barryi as separate species because they remain separate where they occur together in British Columbia, although they are reported to hybridize extensively in parts of Oregon.

The "line" between distinct species and geographical and foodplant forms within a species forms a grey area where there is no "right" answer in some situations. For practical purposes, we draw a line through this grey area, but it is important to recognize that it is there and that the populations may vary in their distinctness, both structurally and genetically, geographically and through time.

The correct name for a species is the oldest name that has been proposed for that species. In some instances a name may be in use in North America and an older name for the same species may be discovered in the literature. This is especially true of our northern species, where names in the Russian literature may be found to apply to species known both from northern Canada and Siberia; for example, in the writings of A.I. Kurentzov, who published a series of articles on the butterflies of the Soviet Far East. The combination of a text written in Russian, rather poor ink-sketch illustrations, and unavailability of the material studied meant that North American workers could not identify the new species proposed by Dr. Kurentzov. Fortunately, J.D. Lafontaine, working with Jim Troubridge, was able to borrow Kurentzov's original Type Specimens from his widow in Vladivostok. These were located by V.S. Kononenko, also of Vladivostok, and transported to Ottawa by Kauri Mikkola via Finland. Study of these specimens by Troubridge and comparison with the type specimens of species described from northern Canada by Troubridge and others leads to the following new synonymies:

Oeneis alpina Kurentzov, 1960 is the correct name for Oeneis excubitor Troubridge, Philip, Scott, and Shepard, 1982.

Oeneis rosovi Kurentzov, 1960 is the correct name for Oeneis philipi Troubridge, 1988.

Oeneis polixenes beringianus Kurentzov, 1960 is the correct name for Oeneis polixenes luteus Troubridge and Parshall, 1988.

SUBSPECIES

Many butterflies vary in appearance in different parts of their geographical range and the use of subspecies categories is our way of placing formal names on this variation. When populations of butterflies look different in geographically separated areas, subspecies classification can be relatively straightforward. In most instances, however, the range of a species, and consequently the variation, is more or less continuous. Frequently, populations in open arid areas like the Great Plains tend to be much paler than populations of the same species from wetter forested areas, and specimens in the northern part of the species range tend to be smaller and darker than those from farther south. To place formal names on this type of continuous and habitat-influenced variation can be endless, with no two specialists agreeing on where limits should be drawn.

At the other end of the spectrum, many western checkerspots and parnassians can look quite distinctive in different mountain ranges and sometimes from colony to colony. Again, there can be problems trying to group this type of variation into subspecies. We do not give a lot of weight to the concept of using formal subspecies names for most types of geographical variation, but we do list and briefly discuss the subspecies names that are currently in use for populations in different parts of Canada.

© 2003. Reproduced with permission from The Butterflies of Canada by Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine. University of Toronto Press; 1998. Specimen photos courtesy of John T. Fowler.