Pterostigma is a character of the order

Pterostigma is a character of the order Odonata.
The pterostigma is a group of specialized cells in the outer wings of insects, which are often thickened or coloured, and thus stand out from other cells.
The pterostigma, a heavier section of the wing than nearby sections, assists in gliding. Without the pterostigmata, self-exciting vibrations known as flutter would set in on the wing above a certain critical speed, making gliding impossible.