Monarch Butterfly - Taxonomy

Taxonomy

The common name “monarch” was first published in 1874 by Samuel H. Scudder because “it is one of the largest of our butterflies, and rules a vast domain”; however, the name may be in honour of King William III of England.

The monarch was one of the many species originally named by Linnaeus in his Systema Naturae of 1758. It was first placed in the genus Papilio. In 1780, Jan Krzysztof Kluk used the monarch as the type species for a new genus; Danaus. Danaus (Greek Δαναός), a great-grandson of Zeus, was a mythical king in Egypt or Libya, who founded Argos; Plexippus was one of the 50 sons of Aegyptus, the twin brother of Danaus.

The monarch is closely related to two very similar species which formed the Danaus (Danaus) subgenus before 2005. The first is the Jamaican monarch (D. cleophile) from Jamaica and Hispaniola. The second is the southern monarch (D. erippus), of South America south of the Amazon river. The southern monarch is almost indistinguishable from the monarch as an adult, though the pupae are somewhat different, and is often considered a subspecies of the monarch proper. But analysis of morphological, mtDNA 12S rRNA, cytochrome c oxidase subunit I, nuclear DNA 18S rRNA and EF1 subunit α sequence data by Smith et al. (2005) indicates it is better considered a distinct species. The separation of the monarch and southern monarch is comparatively recent. In all likelihood, the ancestors of the southern monarch separated from the monarch's population some 2 mya, at the end of the Pliocene. At the time, sea levels were higher and the entire Amazonas lowland was a vast expanse of brackish swamp that offered hardly any butterfly habitat.

Following the review of Smith et al. (2005), two subspecies of the monarch are recognized:

• D. p. plexippus, the nominate subspecies, described by Linnaeus in 1758, is the migratory subspecies known from most of North America.
• D. p. megalippe, named in 1826 by Jacob Hübner, is a nonmigratory subspecies, and is found from Florida and Georgia southwards, throughout the Caribbean and Central America to the Amazon River. Three local forms were at first considered to be other subspecies, but are actually colour varieties of D. p. megalippe:
  • D. p. m. forma leucogyne, named by Arthur G. Butler in 1884
  • D. p. m. forma portoricensis, named in 1941 by A.H. Clark
  • D. p. m. forma tobagi, also named in 1941 by A.H. Clark

Smith et al. did not take up Danaus plexippus nigrippus in their studies. According to Hay-Roe et al. (2007), this taxon is still recognised as a subspecies:

• D. p. nigrippus, named in 1909 by Richard Haensch as forma: Danais archippus f. nigrippus, and is found in South America south of Nicaragua