Species diversity of the extant cycads peaks at 17˚ 15"N and 28˚ 12"S, with a minor peak at the equator. There is therefore not a latitudinal diversity gradient towards the equator but towards the Tropic of Cancer and the Tropic of Capricorn. However, the peak near the northern tropic is largely due to "Cycas" in Asia and "Zamia" in the New World, whereas the peak near the southern tropic is due to "Cycas" again, and also to the diverse genus "Encephalartos" in southern and central Africa, and "Macrozamia" in Australia. Thus, the distribution pattern of cycad species with latitude appears to be an artifact of the geographical isolation of the remaining cycad genera and their species, and perhaps because they are partly xerophytic rather than simply tropical.