Genus Pseudagrion Selys, 1876 (B–group)
Type species: not applicable
The B-group species of Pseudagrion are small to medium-sized (hindwing 14-24 mm), generally paler than those of the A-group, but diverse in the extent of black, bright colours and pruinosity. They inhabit relatively warm habitats, i.e. more often open, stagnant or temporary. Many have broad ecological and geographic ranges.
The following occur throughout Africa, but are relatively common at particular habitats: P. glaucescens and P. hamoni (both at marshy pools and rivers), P. sublacteum (streams, riffles), P. nubicum (larger rivers, lakes) and P. sjoestedti (streams and rivers, often with some forest). Aside from the latter, only P. glaucoideum, P. glaucum and P. isidromorai are partial to the forest of western and central Africa, usually at calm and (partly) shaded waters. The conspicuously yellow P. camerunense is typical of large open ponds and swamps in West Africa, while the diminutive P. aureolum is confined to clear sandy rivers on the Batéké Plateau; P. dundoense is only known from the holotype. P. acaciae (rivers), P. commoniae (pools, sluggish streams), P. lindicum (marshy spots) and P. massaicum (anything marshy) are widespread in eastern and southern Africa. While closely related to the latter, P. tanganyicum has a unique habitat: sandy and rocky beaches and wave-battered reeds in shallows of Lake Tanganyika. Several species are typical of the large marshes and marshy rivers here, especially those in northern Botswana and Zambia: P. assegaii, P. coeleste, P. deningi, P. helenae and P. rufostigma. Especially the first three will perch on vegetation (e.g. lily pads) far from the water’s edge. In north-eastern and western Africa P. niloticum (rivers and streams) and P. torridum (rivers, lakes) occur. P. vaalense and P. pacale are similar in appearance and habitat (large open rivers) to P. acaciae but replace it in the Vaal-Orange system of South Africa and Moa River of Sierra Leone respectively. P. sudanicum is rather localised from its namesake Sudan to western and southern Africa, found at grassy verges of open rivers.
In contrast to the A-group, variation within species can be great. Numerous forms and subspecies have been named, although these seem to have limited practical use, and much variation is age-dependent. For example, all pale areas of the alleged subspecies rubroviride of P. sudanicum are orange at emergence. Abdominal segments 8-9, postocular spots and thorax sides successively become blue, leaving only the face and antehumeral stripes orange. These become brown, the antehumeral may even turn yellow. Moreover, northern males (sudanicum) have a greenish blue face and thin pruinosity on thorax and frons. Similarly, the head and thorax of P. sjoestedti can be bright orange with almost no black, but locally also dull brown, or totally black with pruinose antehumerals. This complexity may conceal unrecognised species. Also appendages (see Pseudagrion A-group for explanation of their structure) vary: typical P. nubicum has a medial tooth on the cerci, which is absent in Zambia and further south. Because of this variation and often small differences in appendages, identification may be difficult. Unlike the A-group, however, the B-group is diverse in the penis shape. [Adapted from Dijkstra & Clausnitzer 2014]
Male of group similar to Pseudagrion A (a) relatively small in size, Hw under 35 mm, Abd under 40 mm; (b) postocular spots often present; (c) transverse ridge on frons absent and Abd never with orange or red, but often with blue; (d) black markings usually more extensive, humeral stripe usually present, if absent body often with blue; (e) Fw quadrilateral with anterior border clearly shorter than distal border; (f) arculus stands at or closer to Ax2. However, differs by (1) apex of S10 bearing black denticles. [Adapted from Dijkstra & Clausnitzer 2014; this diagnosis not yet verified by author]
Map citation: Clausnitzer, V., K.-D.B. Dijkstra, R. Koch, J.-P. Boudot, W.R.T. Darwall, J. Kipping, B. Samraoui, M.J. Samways, J.P. Simaika & F. Suhling, 2012. Focus on African Freshwaters: hotspots of dragonfly diversity and conservation concern. Frontiers in Ecology and the Environment 10: 129-134.
Citation: Dijkstra, K.-D.B (editor). African Dragonflies and Damselflies Online. http://addo.adu.org.za/ [2020-04-05].