Phyllocnistis extrematrix is a moth in the family Gracillariidae. It is found widely in central and southern Europe, and in Kazakhstan and the Asian part of Russia; it has also recently colonised England, where it was first discovered in Norfolk on 29 July 2025.
The larvae feed on several species of poplar, including Populus balsamifera, Populus ÃÂ canadensis, Populus nigra, Populus suaveolens and Populus trichocarpa, forming mines which start near the base of the leaf and then work down the leaf petiole and into young stems.