POPULATION COMPOSITION, GENDER SPECIALIZATION, AND THE ADAPTIVE SIGNIFICANCE OF DISTYLY IN LINUM PERENNE (LINACEAE)

Spatial distribution, pollen-flow and the factors affecting seed-set were studied for a population of the distylous perennial Linum perenne L. during a single season. The morphs were spatially segregated at the site. Stigmatic pollen loads on long-style plants comprised 27 to 51 % legitimate pollen and on short-style plants 0 to 46% legitimate pollen. Most flowers received more legitimate pollen grains than the number theoretically required to fertilize the corresponding number of ovules. Intraflower pollinations accounted for a large proportion of individual stigma loads. There was a weak negative correlation between the distance of the nearest legitimate neighbour and the number of legitimate pollen grains recorded on the stigma. No relationship was established between either the proximity or proportion of legitimate neighbours and seed-set. Long-style plants produced less pollen and matured more seeds than short-style plants. It is suggested that, in the population studied, paternal (pollen) and maternal (seed) investment are unequally divided between the morphs. This may be a common theme associated with heterostyly in plants.