One of the ways in which cycads are identified includes leaflet characteristics, which were not heavily studied when cycads were first identified. In subsequent studies it was found that leaflet width was related to geographic dispersal. Wider leaves typical of "Dioon edule" subsp. "edule" are found in the south whereas the narrower leaves of "D. edule" subsp. "angustifolium" are found to the north. Evidence suggests "D. edule" subsp. "edule" was much more widespread than it is today and became fragmented thus allowing for genetic isolation. It is also speculated that the narrower leaves are endemic in the northern subspecies due to less temperate and humid environmental conditions in these areas.