Pollen release in the Proteaceae

Abstract

Pollen dispersal is the step in higher plant mating systems over which the parent plant has the least control as it is dependent on the vagaries of weather conditions (anemophily) or animal behaviour (animal pollinator activity). While many families have passive release from the anther the Proteaceae has a diversity of pollen dispersal methods. Flowers from a range of species in the Proteaceae, covering the majority of genera from each of the four main subfamilies, were examined to determine how pollen is dispersed and to gain an overall view of how male function varies within the family. This provides a basis for predicting the degree of the six likely fates of pollen released in this family. Only one group (subfamily Persoonioideae) and four genera in one other subfamily (Proteoideae) dispense pollen directly from the anthers onto a flower visitor. Five genera in the Proteoideae have explosive pollen release, while Symphionema may require vibration to release the pollen. All the remaining Proteoideae genera, the single species of Bellendenoideae, and all genera of the Grevilleoideae (except Sphalmium) have a pollen presenter where pollen is dispersed from the style of the flower. Ancestral Proteaceae were likely to have been insect pollinated and had relatively small flowers. Taxa with explosive pollen release may have evolved early in the family and may have been more abundant early in the fossil record. However, the taxa with pollen presenters became much more abundant throughout the Tertiary when many developed robust gynoecia that can accommodate larger vertebrate pollinators.