Amorphophallus mangelsdorffii is described as a species new to science and illustrated. It is closely related to A. antsingyensis as indicated by the spiny (echinate) pollen exine, and both are
more closely related to each other than to the other three endemic species of Madagascar. A. mangelsdorffii differs from A. antsingyensis mainly by the small stigma, much shorter pollen exine spinulae, a reflexed and twisted spathe lamina, amuch less dissected leaf blade with relatively large leaflets and, in contrast to all other Malagasy species, its flowering simultaneous with the leaf at the end of the rainy season. A key to all Malagasy species of Amorphophallus is provided.