Planaeschna ishigakiana Asahina 1951

(Figs 16, 17)

Planaeschna ishigakiana guentherpetersi Sasamoto, Do & Vu, 2013 stat. nov.

Planaeschna guentherpetersi: Sasamoto et al. (2013) pp. 587–590, Figs 1–10.

Materials examined. 1 ♀, Xuan Son NP, Phu Tho Prov., 26-X-2013, TK leg.; 1 ♂ 1♀, same location and collector, 26-X-2014; 2 ♀♀, same location and collector, 23-XI-2014; 2 ♀♀, same location and collector, 29-XI-2014; 1 ♀, same location and collector, 11-X-2015.

Notes. Sasamoto et al. (2013) compared P. guentherpetersi with other species with rich brown facial colour (Fig. 16A, C) in their diagnosis of the species, but not with species with more colourful faces. The dorsal pattern on S2 (Fig. 16E–F) is unique among Vietnamese Planaeschna species (but see Planaeschna sp. 2 below, and Fig. 18C). However, this pattern occurs in several species recently described from continental China, and is also found in P. ishigakiana from Japan and Taiwan. Three subspecies are known for P. ishigakiana: nominotypical P. ishigakiana was described from Ishigaki-jima, and later recorded also from nearby Iriomote-jima, of the Yaeyama Islands in the Ryukyu archipelago of Japan, just east of Taiwan. The subspecies P. i. nagaminei Asahina, 1988 was described from Amami Oshima, Ryukyu archipelago of Japan, followed by the description of P. i. flavostria Yeh, 1996, from Taiwan. The three subspecies of P. ishigakiana are different in patterning, but structurally identical. All three have a more colourful facial pattern. Sasamoto et al. (2013) did not compare their P. guentherpetersi to P. ishigakiana for their diagnosis, which was reasonable in view of the different facial pattern and in view of the large distributional gap between these species, even if the pattern on S2 was the same.

Our DNA analysis suggested that the three known subspecies of P. ishigakiana not only clustered well with slight differences, but surprisingly, that specimens of P. guenterpetersi were also included in the same clade, suggesting that they were the same species.

In fact, P. guentherpetersi not only has the same pattern on S2, but also identical anal appendages to those of P. ishigakiana (see Fig. 17 for a comparison of Planaeschna guentherpetersi from Xuan Son with drawings by Asahina (1988) of P. i. ishigakiana and P. i. nagaminei). The three known subspecies of P. ishigakiana are geographically isolated: the Yaeyama Islands are about 200 km from Taiwan and over 650 km from Amami Oshima. It is therefore not surprising that these populations display some differences in colouration. Although specimens currently identified as P. guentherpetersi likewise shows some differences in colouration compared to the other three subspecies (see diagnosis below), the DNA and morphological evidence presented here shows these are in fact conspecific with specimens belonging to P. ishigakiana. Asahina (1988) and Yeh (1996) gave precedence to structural similarities over differences in coloration between these taxa when determining specific status. We concur with their approach and therefore treat this taxon as a fourth subspecies: P. i. guentherpetersi stat. nov.

To our knowledge, this is the first known example of a species within this genus with such a large disjunctive range consisting of isolated populations that differ distinctly in patterning.

Differential Diagnosis. The male of this subspecies differs from the other subspecies by the largely brown facial pattern lacking clear black and yellow markings (Fig. 16A), the more brown rather than black tones of the dark parts of the pterothorax (Fig. 16B) and from P. i. flavostria by its darker maculation (Fig. 16B). The female differs by the all brown face (Fig. 16C) and the lateral pattern of S2 (Fig. 16D).

Ecology. This is the most common Planaeschna in Xuan Son NP, where it inhabits shallow streams under heavy forest cover. Females were observed during the day ovipositing in rotting wood just above the water surface, or hung up in nearby trees. Males were rarely observed. All records were from October and November.

Distribution. Japan (Yaeyama Islands (P. i. ishigakiana), Amami Oshima (P. i. nagaminei)), China (Taiwan (P. i. flavostria)), Vietnam (Phu Tho Prov. (P. i. guentherpetersi)).