The specific epithet oppositifolia is derived from the Latin oppositus which means ‘opposite’ and folium meaning ‘leaves’ and refers to the arrangement of the leaves, which is opposite.

The taxonomic history of Gnidia oppositifolia is complex, reflecting the historical development of taxonomy of plants in southern Africa. In 1753, the species was described for the first time by Carl Linnaeus, who placed it into the genus Gnidia based on its morphology: opposite leaves and tubular flowers, which served as key taxonomic features. From the middle of the eighteenth untill the beginning of the nineteenth century, Gnidia oppositifolia continued to belong to the genus Gnidia, although during that period, several synonyms were described based on morphological variation observed among different populations of this species. In the twentieth century, after advancements in comparative morphology, discussions regarding the circumscription of Gnidia became more common, with some botanists arguing that several Gnidia species, should be classified as Lasiosiphon due to their close relationship. Finally, in the late twentieth and early twenty-first centuries, when phylogenetic analyses based on molecular data proved Gnidia to be polyphyletic (containing unconnected lineages), those discussions gained even more momentum. The last revision by Olaniyan et al. in 2024, based on molecular and morphological data yielded compelling arguments for moving tropical African Gnidia taxa into Lasiosiphon, which marks an important step in the taxonomy of these genera. The new classification marks the end of more than two centuries of research in botany and reflects the transition from traditional morphology-based classification to modern genetics-based classification.