The Eye of the Flower - Annulate vs Exannulate

The eyes are the window of the soul.

The eye of a Primula flower is its center which may be colored different from the rest of the corolla and which is the mouth or end of the flower tube containing the stigma or anthers (see Style Position).

In Primula, whether the flower is annulate or exannulate is an important characteristic to differentiate between species.
Close-up of the annulus in a Primula flower
Annulate means having a ring-like constriction (annulus) at the mouth of the flower. A different colored eye from the rest of the corolla does not indicate that an annulus is present. Some species even may be weakly annulate or sometimes exannulate. Exannulate is the opposite; no annulus is present. The best way to determine whether an annulus is present is to slice open the flower.

Slice open a flower to determine annulate (L) vs exannulate (R).
Examples of annulate Primula flowers 
Examples of exannulate Primula flowers


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