Anthesis means

Anthesis means the opening of a floral bud.
Anthesis is the period during which a flower is fully open and functional. It may also refer to the onset of that period.
Anthesis of flowers is sequential within an inflorescence, so when the style and perianth are different colours, the result is a striking colour change that gradually sweeps along the inflorescence.
Flowers with diurnal anthesis generally are brightly colored to attract diurnal insects, such as butterflies.