Reproductive biology ofGeranium sessiliflorum. 1. Flower and flowering biology

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Abstract
Flower and flowering biology of Geranium sessiliflorum were investigated using a combination of field and greenhouse observations. The flowers were shown to be protandrous at one locality, homogamous at another, and protogynous at a third locality. The length of the male stage of protandrous flowers may differ not only from plant to plant but also between flowers on the same plant. These differences in the timing of the female and male stages are maintained in cultivation. Pollination experiments revealed flowers to be automatically selfing with a seed set as high as that following cross-pollination. In all experiments and in the field, 25–70% of the flowers did not set seeds. Of flowers that produced seeds, around 50% had five seeds. A rate of cross-pollination of 16% was estimated from emasculated flowers in the field. The most frequent visitors were ants and mites. The breeding system is considered to be facultatively autogamous. The number of open flowers per day per plant from plants of different size was noted. The chance of a plant on a particular day having open flowers increases with its size. In all features studied, no difference between the three leaf colour morphs was found, but there were significant differences between the localities in flower biology and seed set.