Diagnostic seed surface morphologies have been identified in some members of the family Plantaginaceae; however, limited diagnostic seed morphologies have been identified in the subtribe Gratiolinae of tribe Gratioleae. Tribe Gratioleae consists of 25 genera and about 182 species distributed worldwide. Ten genera are classified under subtribe Gratiolinae. The current study employed scanning electron microscopy (SEM) to examine detailed surface sculpturing in the subtribe Gratiolinae to identify diagnostic seed characters of taxonomic significance. Seeds of 35 species representing seven genera were carefully sampled from herbarium specimens, mounted on aluminum stubs, observed under the SEM, and analyzed. Seeds were typically less than 1.0 mm in size. Eleven reticulate seed types were identified with significant variation. Variation resulted from at least five characters: overall seed pattern, seed length, periclinal wall ornamentation, anticlinal wall relative height, and ornamentation. Most seed types were characteristic of genera. Seed types of Bacopa did not correspond to sectional treatment of the genus and seed type observed for the monotypic segregate genus Benjaminia was shared with some members of Bacopa. Seed types identified for the segregate genus Mecardonia were not observed in Bacopa, whereas similar seed types were observed between some members of Mecardonia and the monotypic genus Amphianthus. The diversity in seed surface morphology suggests extensive but taxonomically significant seed variation in the subtribe Gratiolinae.