Lotic dragonfly (Anisoptera: Odonata) nymphs of the Southeastern United States: identification, distribution and historical biogeography

An identification guide to the southeastern United States lotic dragonfly nymphs is constructed. Descriptions, figures, keys, verification tables, and distribution maps are provided to facilitate identification of families, genera, and species. Information developed in the study of nymphs is utilized to evaluate arrangements of taxa that have been traditionally based solely on adult characters. Traditional arrangements are supported except (1) subgenera of the genus Gomphus s.1. are highly distinctive in the nymphal stage and should be elevated to generic rank and (2) two species, Gomphurus consanguis and G. rogersi are improperly placed and as a group deserve generic rank.

A study of ranges of North American species led to an analysis of the historical biogeography of the genera. An analysis of the worldwide distribution of genera of the North American fauna led to the following conclusions: (1) the Nearctic fauna is composed of relicts of a once continuous Holarctic Tertiary fauna, a few Jurassic relicts, and minor lineages derived from the Neotropical realm, (2) species of the modern fauna are considered to have differentiated by late Tertiary or early Pleistocene times and (3) certain other nominal species or yet unrecognized taxa are considered of subspecific rank and of late Pleistocene age.