What is the difference between pin-eyed and thrum-eyed primroses?

http://en.wikipedia.org/wiki/Primula_vul...

http://en.wikipedia.org/wiki/Oenothera

What is the difference between pin-eyed and thrum-eyed primroses?
In pin-eyed flowers, the stigma is at the top of the flower tube and can be seen in the centre of the flower looking like a small green pin head. In this type of flower, the anthers are halfway down the central flower tube, in a ring around the style.



In the thrum-eyed type, the style reaches only halfway up the flower tube, so that the stigma is also positioned halfway up inside the tube. The anthers in this type are at the top of the flower tube and can be seen as a yellow/orange mass in the centre of the flower.

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