An Australian endemic, Hemicordulia tau is known from every state/territory including Tasmania. Whilst being called an Emerald, it doesn’t actually resemble any of the European Emeralds with which I’m familiar. Though the dark markings on the abdomen can look like metallic British Racing Green in certain lights, the name has more to do with the fact that it is one of the Corduliidae.
We found ours ranging around Beechworth and Stanley at a number of sites. We never saw a male settle so the only option was in-flight shots. Much later, we ran across a grounded teneral female.
Differentiation from the very similar Hemicordulia australiae (Australian Emerald) centres around the black T-mark topping the frons, hence its name, tau being greek for T.