Cryptantha arenophila Rebman & M.G.Simpson (Boraginaceae) is described as new. This species is restricted to sandy dunes near San Quintín, Baja California, Mexico and adjacent coastal regions. It is similar to the more common Cryptantha patula Greene in stem vestiture, calyx morphology, and inflorescence morphology. Cryptantha arenophila differs from that species in having significantly larger corolla limbs and narrowly oblong to narrowly elliptic leaves with obtuse-rounded leaf apices, as opposed to linear to narrowly lanceolate leaves with acute to obtuse leaf apices in C. patula. In addition, nutlets of C. arenophila tend to have more numerous and shorter tubercles, while those of C. patula have tubercles that are less dense and larger, although variation in this species needs further investigation. The dune habitats where the type locality of C. arenophila occurs are currently under severe impacts from animal grazing and off-road traffic, necessitating the conservation of these regions.