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The flowers of the arctic poppy (Papaver radicatum L.) track the sun, and the petals of the flowers reflect light towards the ovary. This study investigated the importance of petals to reproductive success in this species. We measured light intensity, ovary temperature, seed weight, and number of seeds produced by flowers that had their petals removed versus flowers with their petals intact. Flowers without petals do not track the sun. Irradiance was greater when the photocell was held coincident with the angle of sun-tracking flowers than when facing upward. Flowers with petals had significantly higher overy temperatures both at the ovary surface and in the ovary interior than did flowers lacking petals. In pairs of flowers on the same individual plant, those with their petals removed had significantly fewer and smaller seeds than control flowers with petals intact. There were site differences in the significance of the treatment effect, but not in the magnitude of the differences between flowers with and without petals. Therefore, the presence of petals resulted in increased irradiance and temperature at and in the ovary, which affected reproductive success. Key words: heliotropism, Papaver radicatum, petals, reproductive success, temperature.

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