Hypotrachyna angustissima is a species of lichenized fungi within the Parmeliaceae family. This species is characteristic by the occurrence of usnic acid in its cortex, and salazinic acid in its medulla and laminal isidia. In this it resembles Hypotrachyna microblasta, but the latter has wider laciniae and larger apothecia, and is laterally overlapping. Its epithet angustissima is derived from the Latin angusti, meaning "narrow", due to this species' very narrow laciniae.