A new species of Fritzschia is described and compared with its probable relatives. Fritzschia rupestris is characterized by its sprawling habit with elongate internodes, absence of trichomes on vegetative and floral organs, ovate to subcordate glutinous leaf blades with serrulate margins, solitary pedunculate flowers, magenta petals, dimorphic stamens with well-developed staminal appendages, calyx lobes that become thicker in fruit, and ovary apex with a few scattered sessile glands. Diagnostic line drawings, field images, SEM photos of seeds, a distribution map, and a conservation assessment are provided, along with a key to all the species currently recognized in the genus Fritzschia.