Characterization and distribution of the species included in the genus Thecagaster Selys (Odonata: Cordulegastridae)

Cordulegastridae Tillyard, 1917 is an enigmatic Odonata family with mainly Holarctic distribution. One of its five genera is Thecagaster Selys, 1854, a genus restricted to smaller brooks, trickles, or seepages in the spring or near the spring regions in moderated high mountain areas of the Palaearctic Region. Because of their phenotypic similarity, some species within this group were confused for many decades and have only recently been well characterized with the help of molecular genetic methods. Therefore, the exact reconstruction of the distribution patterns of the members of the genus was not possible until recently. Here, we characterize the genus Thecagaster and all its known members and construct the distribution maps on the basis of published data and internet platforms. Some hybrid and introgression zones at the distribution limits between some species are also discussed. The information given here will assist field workers in better identifying these partially endangered species and also helps to protect them.