Variation of pollen limitation in the early flowering Mediterranean geophyte Narcissus assoanus (Amaryllidaceae)

A recent literature review indicates that pollen limitation of female ferti lity is a common feature of flowering plants. Despite the ecological and ev olutionary significance of pollen limitation, most studies have only examin ed fertility in a single population at one time. Here we investigate pollen limitation of fruit and seed set in five populations of Narcissus assoanus , a self-sterile, insect-pollinated geophyte, over 2-3 years in southern Fr ance. In common with many early spring flowering plants, pollinator visitat ion to N. assoanus is often infrequent. Supplemental hand-pollination of fl owers with outcross pollen significantly increased overall fruit and seed s et by 11% and 19%, respectively. Four of the five populations experienced s ome pollen limitation during the study. For a given year, there was signifi cant variation in pollen limitation among populations. Two of the populatio ns were pollen limited in one year but not in other years in which they wer e studied. Seed:ovule ratios for open- and hand-pollinated flowers averaged 0.29 and 0.33, respectively. While hand pollination significantly increase d the seed:ovule ratio, the low value obtained indicates that the majority of ovules in flowers do not mature seeds despite hand pollination. The role of genetic and environmental factors governing low seed:ovule ratios in N. assoanus is discussed.