Persoonia glaucescens, commonly known as the Mittagong geebung, is a shrub native to New South Wales in eastern Australia. It was formerly known as Persoonia lanceolata subspecies B. It is currently classified under Commonwealth legislation as vulnerable, and is listed in New South Wales legislation as endangered. Within the genus, it is classified in the Lanceolata group, a group of 58 closely related species with similar flowers but very different foliage. These species will often interbreed with each other where two members of the group occur.