Moths in the genus Probole are common in woodlands throughout much of the Nearctic Region. Transcontinental in Canada and northern plain states, its range extends from British Columbia to northern California and in every state east of the Mississippi River. Classification within the genus is historically problematic and authors since the 1850's have proposed a diversity of names, recognizing from one to four taxa. To resolve this uncertainty, this study used morphological, molecular, and developmental information to quantify patterns of variation and their relationship to sex, brood, and geographical distribution. Morphological study of museum specimens emphasized cuticular features of genitalia and wing patterns in both sexes. Developmental studies documented variation in F1 progeny from isofemale rearings of known morphological type. Molecular studies measured sequence divergence in the mitochondrial COI gene from various geographical regions, seasonal broods, and morphological types. Several morphological types were reared from isofemale cultures, indicating a lack of support for a classification that includes more than one species. COI sequence data show relatively low intrageneric divergence (<2.8%) when compared to other closely related geometrid moths, again indicating a lack of support for recognition of more than one species. As a result of these findings, the genus Probole is treated as containing a single, highly variable species, Probole amicaria (Herrich-Schäffer). This species exhibits within-population polymorphism, sexual dimorphism, between-brood polyphenism, and is also geographically polytypic.