The genus Mollugo L. comprises ca. 35 species distributed throughout the tropics, and it is clearly polyphyletic. The seed morphology and ornamentation of 27 Mollugo representatives is studied with regard to their significance for systematics and taxon delimitation. The species belonging to the “M. cerviana” and “M. fragilis” groups, as well as M. tenella, are characterized by D-shaped or roundish seeds, whereas other taxa have reniform seeds. The seed ornamentation can be considered to be one of the most valuable characters for disentangling the taxonomic diversity in the genus. Mollugo cerviana shares the same reticulate ornamentation with M. namaquensis, M. pusilla, M. tenella and M. tenuissima, while the smooth surface is peculiar to M. fragilis, M. spathulata and M. walteri. The close relationship of M. fragilis and relatives to Hypertelis spergulacea is carpologically supported. Some taxa share a papillate ornamentation (M. decandra, M. floriana, M. molluginis, M. nudicaulis, M. pentaphylla, M. pentaphylla var. rupestris), but this character appears to be a homoplasy in the light of existing molecular phylogeny. The “Mollugo nudicaulis” group (M. angustifolia, M. cuneifolia, M. decandra, M. nudicaulis s.str., M. nudicaulis var. navassensis) as well as M. molluginis from the “M. pentaphylla” group have foveolate cell boundaries. Seed ornamentation can be an additional character supporting reinstatement at species rank of the forgotten New Caledonian taxon M. digyna, as well as Caribbean M. nudicaulis var. navassensis. Mollugo pentaphylla and M. verticillata are found not to be uniform in seed characters. The endemics of the Galapagos archipelago that have been studied (M. flavescens, M. floriana, M. gracillima, M. snodgrassii) differ in their ornamentation from M. verticillata. Mollugo tenella is distinguished from all other species in having short, trichome-like depositions of epicuticular wax on the seed surface. The discovered carpological characters can be important for the delimitation and taxonomy of different Mollugo groups.