Phyllotactic pattern is altered in the transition to flowering in the early ears of Zea mays landrace chapalote (Poaceae).

The origin of polystichy in the maize ear and central tassel spike continues to challenge our understanding of evolution in this important crop species. In this paper we tested the hypothesis that the change in phyllotaxy occurs in the region of husk leaf production before the transition to reproductive growth. Young ear or presumptive ear primordia were dissected to examine the transition from distichous husk leaves below the ear through spiral phyllotaxy to the polystichous arrangement of spikelet pair primordia in the young ear. Serial transverse sections were used to document the thickness of successive disks of insertion of lateral primordia and to reconstruct the path of procambial differentiation. The transition in phyllotaxy, though variable, typically occurs in the vegetative zone and is associated with periodic heterogeneity in the thickness of leaf bases and a delay in the development of waves of procambial differentiation into the base of the young ear.