How flower biology and breeding system affect the reproductive success of the narrow endemic Polygala vayredae Costa (Polygalaceae)

Polygala vayredae is a narrow endemic species from the oriental pre-Pyrenees. Despite its conservation status and rarity, no information is available on its reproductive biology. As the flower is the structure directly involved in pollinator attraction, its morphological and functional traits have major effects on the reproductive success of the plant. In this work, the flower biology and breeding system of P. vayredae were studied to evaluate how they affect the reproductive outcome in natural populations. Flower morphology, flower rewards, and male and female functioning throughout the lifespan of the flower were assessed. Pollination experiments, involving pollinator exclusion and pollen from different sources, were conducted, and the pollen ovule index was determined. Female fitness and the occurrence of pollen limitation were assessed in three natural populations over 2 years by observing the presence of pollen on the stigma, pollen tube development, and fruit production. Polygala vayredae flowers are elaborate and long-lived with nectar rewards. The floral traits are well adapted to xenogamy and entomophily, which are in accordance with the observed breeding system and auto-incompatibility system. No mechanism of reproductive assurance was observed and P. vayredae strictly depends on pollinators to set fruit. Low fruit production was observed in the studied populations, which was largely the result of scarce, unreliable, and/or inefficient pollinators and poor pollen quality. In addition, available resources may be a limiting factor. The reproductive strategy of P. vayredae prevents inbreeding depression by a self-incompatibility system, which in years of scarce pollinators is overcome by the plant habit. (c) 2008 The Linnean Society of London.