Collinsonia (Lamiaceae) is a small genus restricted to eastern North America with four species commonly recognized: C. canadensis, C. serotina, C. tuberosa, and C. verticillata. Considerable taxonomic confusion exists within subgenus Collinsonia (all taxa except C. verticillata). Principal components and canonical variates analysis were performed on a macromorphological dataset of 23 variables scored for 118 specimens of subgenus Collinsonia. Results from field and herbarium observations and from the phenetic analyses indicate that specimens of C. serotina with four stamens (hereafter referred to as C. anisata) represent a distinct species. Specimens of C. serotina with two stamens are intermediate between C. canadensis and C. anisata and are tentatively recognized as C. punctata; further study is needed to determine their origin and evolutionary status. Collinsonia tuberosa and C. canadensis show considerable phenetic overlap and are here merged under C. canadensis. Four species of Collinsonia are now recognized: C. anisata, C. canadensis, C. punctata, and C. verticillata.