Phacelia ranunculacea sensu lato (subgenus Cosmanthus, Hydrophyllaceae) occurs on floodplains and in alluvial hardwood forests throughout eastern North America. It is comprised of herbaceous annuals with alternate, pinnate leaves and white to lavender, tubular-campanulate flowers in terminal scorpioid-like cymes. The distribution of populations displays a disjunct between the Midwest and Atlantic coastal plain, with a chromosome number of n = 6 associated with the former and n = 14 allied with the latter. A phenetic analysis of morphological characters was conducted using 350 herbarium specimens examined from 21 herbaria. The resulting phenogram revealed two distinct clusters of specimens that correspond to the haploid chromosome numbers. Correlation of the clusters and chromosome counts with type specimens resulted in recognition of two taxa: Phacelia ranunculacea sensu stricto and Phacelia covillei. Results of morphological analyses, a diagnostic key, species descriptions, and lists of representative specimens are provided for these two closely related species.