In Argentina Ocimum is represented by four species: Ocimum campechianum, Ocimum nudicaule, Ocimum ovatum, and Ocimum selloi. Complete descriptions for each of these taxa and illustrations, as well as a key for their identification, together with distribution maps in Argentina are given. Four new synonyms are here proposed, and lectotypes are here designated for the following species: Lumnitzera carnosa, Ocimum balansae, Ocimum hassleri var. acutatum, Ocimum micranthum, Ocimum neurophyllum, O. nudicaule, O. ovatum, O. selloi, O. selloi var. angustifolium, O. selloi f. serratum, and O. selloi f. subintegrifolium.