This is the most common and widespread species of Spermacoce in Madagascar, where it seems to be quite weedy. It has been collected often though not exclusively on white sand substrates, and frequently in dry and littoral forests. In addition to the protected areas compiled by the Mad.Cat. project, this species is documented from the Parc de Tsimbazaza.
The range of this species is here described as including Africa because there are no evident differences between the plants of Madagascar and the associated islands, and the plants of eastern Africa that are treated as Spermacoce huillensis (Hiern) Good. The geographic origin of this species is unknown, and could be in either continental Africa or the Madagascar region; the problem of its origin mainly affects whether the species is considered native or introduced. It is widespread in Madagascar and the Comores, and is here assumed to be naturally occuring in these islands for now.
This species has been confused with Spermacoce pusilla, which has been collected only infrequently in Madgacar. Spermacoce flagelliformis generally grows as a taller plant with longer internodes, and the leaves are borne in pairs along the stems and usually narrowed gradually to the base (i.e., narrowly elliptic and sometimes apparently petiolate) and the capsules are appressed-strigillose; while Spermaacoce pusilla is usually a ahorter plant that appears bushy due to the growth of "supernumerary" leaves from the unexpanded axillary buds, and the leaves are variable in form but often are straight-sided almost to the base and then only shortly abruptly narrowed (often giving them an appearace of lanceolate and sessile), also the capsules are hirtellous with spreading trichomes.