Breeding system and seasonal variation in seed set in a population of Potentilla palustris

Abstract

The breeding system and factors affecting seed set in a population of Potentilla palustris were studied in Central Jutland, Denmark. The reddish-brown, bowl-shaped, and nectariferous flowers of Potentilla palustris had an average of 376795 viable pollen grains and 187 single-ovuled carpels. The number of ovules per flower decreased significantly along an inflorescence, from 312 in the basal flowers to 97 in the flowers in distal positions. The flowers were protandrous and opened mainly during the day. Male and female phases lasted on average 1.6 and 3.0 days, respectively. Pollination experiments showed that P. palustris was facultatively autogamous to facultatively xenogamous. The plant was selfcompatible and auto-deposition of pollen occurred, but insect polllination enhanced seed set. Outcrossing increased seed set compared to selfing. A long outcrossing distance increased seed set comparative to short distance crossings. Seed set per flower declined through the flowering season mainly due to a significant reduction in the number of ovules per flower with time and/or node position. It is suggested that intra-plant competition for a limited amount of resource is the main factor limiting seed set in this population, but pollen limitation occur in late season. The quantitative and qualitative impact on seed set by pollinating insects is discussed.