Reproductive biology of the rare biennial Gentianella germanica compared with other gentians of different life history

We tested reproductive biology and pollination limitation of the rare Gentianella germanica in two large populations in The Netherlands, at the margin of its distribution area. Gentianella germanica is self-fertile, but pollinators are essential for the transport of pollen to the stigmas. In caged and untouched flowers the mean seed set was reduced to less than 30%. However, the ability of auto-deposition of pollen on the stigma varied between individuals (0-90%). The reduced seed set after hand-selling in one population indicates some inbreeding effects on ovule or seed abortion, but in the other population no inbreeding depression was observed. This population had an overall lower seed set and seed number per fruit. Despite the favourable nutrient conditions, and higher number of ovules per flower in this population, there was apparently a limit to the number of seeds that could be matured per fruit. There was no evidence for pollination limitation in either population. A comparison of autofertility and ovule production per flower with several other gentian species differing in life history confirmed the hypothesis that the annual and most gentians are selfers and the perennials predominant outcrossers. Hence, particularly the perennial gentian species risk reductions of reproductive success and inbreeding depression owing to habitat fragmentation and pollination limitation. In contrast to other biennials, G. germanica was more similar to the perennial species, because of its poor autofertility. The possible role of herkogamy and dichogamy in the varying ability of individuals to self-pollinate spontaneously is discussed, and will be studied in the near future.