Further assessment of pollen limitation in the waratah (Telopea speciosissima)

The literature contains much debate about whether pollen limitation results in a cost to plants. A population of the waratah, Telopea speciosissima (Proteaceae), was found to be pollen limited in 1985. The present study examines the consequences and causes of this pollen limitation. In the 2–3 years following the original experiment, there was no difference in vegetative growth, flower production or fruit production between the hand-pollinated or control plants. There was no difference in inflorescence or fruit production between these two plant groups up to 9 years later. There was no cost of the experimental increase in reproduction. Experiments in 1988 failed to reveal further pollen limitation, suggesting that it may only occur in some years in this population. The retention of self-pollen on stigmas after anthesis was implicated as a cause of the original demonstration of pollen limitation because the waratah is self-incompatible, has highly synchronous flowering and, typical of the Proteaceae, deposits self-pollen on its stigmas at anthesis. These traits should provide a continuing influence on fruit set in all years. However, plants did not produce more fruits when the self-pollen was experimentally removed. This suggests that the waratah experiences pollen limitation in years when pollination and nutrient levels are not in equilibrium. Further studies of pollen limitation are required to fully understand the fitness consequences of this phenomenon, and to fully describe its frequency among different plant families and among plants with differing flowering strategies.