Miconia rheophytica is described, illustrated, and compared with presumed relatives in the Octopleura clade. It is distinguished by its narrowly elliptic to ovate-lanceolate leaf blades with entire to subentire margins that have evenly spaced spreading smooth eglandular trichomes 0.8−1.4 mm long, an indumentum of dendritic trichomes with short axes and terete radiating arms on distal internodes, adaxial petiole surfaces, and primary and secondary veins on abaxial leaf surfaces, unribbed hypanthia that are constricted and tapered distally below the torus and covered with a mixture of basally roughened trichomes and dendritic trichomes with short axes, anthers with two ± truncate apical pores, eglandular anther appendages, 3-locular ovary, and berries that are bright blue at maturity. It is known only from flash-flooded riverbanks in three river canyons in the Magdalena Medio region of Antioquia, Colombia. A conservation assessment of “Endangered” is recommended for this species based on IUCN Red List Categories and Criteria.