Abstract: The bracing and merging pattern of basal longitudinal veins plays an important role in phylogeny reconstruction within Pterygota. Unfortunately, the basal venation pattern of living mayflies has changed from the ancestral state in most species, but in very rare cases, the origins of some longitudinal vein bases are preserved and visible. The wing base of Siphluriscus chinensis has an independent subcostal brace, partial stem of the media, visible stem of the cubitus, and indications of the origins of MA and Rs. This kind of wing base plus those of Ephemera rufomaculata and Chromarcys magnifica show the venation groundplan of modern Ephemeroptera (stem of M parallel to or fused with R basally, MA and Rs fused together for certain distance then separate, Cu independent at base). This pattern seems close to that of Neoptera while different from Odonata. In the latter, the M fused with Cu basally. The hypothesized function of subcostal brace in mayflies is to strengthen the connection between distantly separated longitudinal veins because of sclerite plate at radius vein base. This hypothesis also can be used to explain complicated and unique venation of dragonfly.

Key words: Ephemeroptera, Odonata, Neoptera, vein, wing, phylogeny, flight, dynamics