Palaeocene
The warm Paleocene climate, much like that of the Cretaceous, supported  polar forests. Rainfall is a major factor in plant diversity nearer the equator, but polar plants have to adapt to light (polar nights and midnight suns) and temperature. Because of this, plants from both poles evolved some similar characteristics, such as broad leaves. Plant diversity at both poles increased throughout the Paleocene, especially at the end, with the increasing global temperature.