Both accepted spp are inadequately known, and unfortunately collections of Ptisana generally lack crucial information that is necessary to adequately differentiate species in the genus, judging from what is known of species occurring in Africa which are somewhat better known (Senterre, pers comm.). Collectors are encouraged to make careful observations on:
- dimensions of the leaves
- size relative length of the petiole and the leaf rhachis (i.e. the leaf axis excluding the petiole)
- number of pinnae
- present of tertiary division or lobing of some of the leaves
- the colour of the "flesh" of the petiole and rhachis
Careful study of the plants in the field is required to confirm the delimitation of the 2 known spp, and to develop a more reliable account of species diversity in Madagascar for the genus.