Anthesis is the opening of a flower, or the interval during which it is open and functional. It is a developmental stage within flowering, which also includes the earlier transition to making flowers. A flower bud can therefore be present before anthesis.[ref]
The distinction is useful in an experiment: comparing two flowers three days after anthesis aligns their development more closely than comparing them three days after their parent plants were moved to a greenhouse. Opening does not by itself establish that pollination or fertilization has occurred. Those are separate events whose timing must be observed.
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