Phyllanthus comprises approximately 1,270 species, making it one of the world's largest plant genera. Molecular data so far are of limited value for understanding Phyllanthus because of the sheer size of the genus. They can, however, help sort-out cryptic species and provide information on the origin of suspected introduced species. One of the seemingly most widespread species is P. reticulatus, which has been recorded from Asia, Australia, Africa, and Jamaica. The name is based on a mixed collection from tropical Asia now in the Lamarck herbarium, and we lectotypify it here. We use nuclear ITS sequences to test the broad treatment of P. reticulatus in recent floras, identify records of “P. reticulatus” from Africa, and investigate the origin of P. reticulatus on Jamaica. A maximum likelihood tree for accessions of P. reticulatus from throughout its supposed range (plus relevant outgroups) shows that the Jamaican plants represent the Asian species, that the African plants called P. reticulatus belong to a separate clade for which P. polyspermus is the oldest available name, and that the sensu lato treatment of P. reticulatus in recent floras is unjustified. Treating the Asian entities P. reticulatus and P. microcarpus as separate species appears justified, and identical ITS sequences in Asian and Jamaican P. reticulatus indicate a recent introduction. The first “island botanists,” J. Macfadyen and N. Wilson, introduced many plants from India in the 1800s, and theirs are the oldest Jamaican collections of P. reticulatus. Since the species was introduced to Jamaica without its obligate Epicephala moth pollinators, it does not set fruit, persisting instead by vegetative growth.