The unique inflorescence structure of Dorema aucheri (Apiaceae): An adaptation to the arid environment

摘要

Arid environments demand specific adaptations from plants in vegetative and reproductive systems. Self-compatibility, high pollen production and few well developed fruits are adapted to increase sexual reproductive success. Dorema aucheri is an arid-adapted, perennial monocarpic species endemic to southern Iran. It has a unique inflorescence structure. In this study, significance of inflorescence architecture for reproductive success was investigated in a wild population. The huge yellow inflorescences were frequently visited by manifold insects. The species is andromonoecious and spatially subdivided in a distal part with perfect flowers and a proximal part with male flowers. Flowers are protandrous and synchrononized in a duodichogamous manner which starts with the male, then female phase of the perfect flowers, followed by the male phase of the remaining flowers (7-10 days). Bagging assays confirmed that the plant is self-fertile. Sexual phases partly overlap allowing geitonogamy at some days and demanding obligate outcrossing at other days. The mixed breeding system and high degree of andromonoecy (77 +/- 31%) coupled with an immense surplus of pollen grains (P/O = 261,991:1), the long male flowering stage, attraction of flying pollinators by massive flowering and sexual asynchrony between neighboring plants are interpreted as adaptations to the arid environment increasing the rate of outcrossing.