Primulas (1) (2) have two distinct types of flowers on the same plant: pin-eyed and thrum. In a pin-eyed flower, the stigma is positioned above the anthers. The stigma is rounded and pin-shaped, dominating the throat's opening. This position of the style prevents self-pollination, as the pollen from the anthers cannot reach the stigma. In contrast, a thrum flower allows self-pollination because the anthers are situated above the stigma. A plant that bears both types of flowers is called a heterostyle flower.