For the first time, histochemical and cytotoxic studies of Bathysa australis (A.St.-Hil.) K.Schum. (Rubiaceae) were investigated. Leaf micromorphology and histoanatomy were detailed and recorded by optical, transmission and scanning electron microscopy. The species also exhibited a dose-dependent viability and apoptotic effect on leukemic and colorectal cancer cells at all tested leaf extract concentrations. The histochemical results reinforce that this plant provides a new source for secondary metabolite classes: alkaloids, anthraquinones, coumarins, polyphenols and saponins, which may be able to induce apoptotic death of cancer cells. Scientific studies can be directed to investigate the interference of different environments in which B. australis is adapted, the histochemical and anatomical foliar variations and the relation with the phytochemical bioactivity of this Rubiaceae on U937 leukemic cells and COLO-205 colorectal cells as well as other human tumor cell lines. © 2022 SAAB