Buzz pollination in the Epacridaceae

Abstract

Conostephium (Epacridaceae) has flowers that conform with a buzz-pollination syndrome but, unlike most plants with this form of pollination, the anthers are hidden within the corolla tube. Vibrations generated by bees grasping the apices of the corolla tubes must be transferred via short broad filaments to the anthers. The anthers do not have pores but each dehisces from the apex by a slit that elongates over the time the flowers take to senesce (up to 10 days). This may limit self-fertilisation as the stigma is receptive as soon as it appears from between the very short corolla lobes, so little pollen is released at first but later this would increase as the slit elongates. Visitation by pollinators has rarely been seen but several observations of native bees (Leioproctus and Lasioglossum) working the flowers are presented. The bees visit the nectarless flowers of Conostephium only for pollen and must forage at other kinds of flowers to obtain nectar. Pollen tubes occurred in the stigmas of most older flowers of C. pendulum, so pollen delivery does not seem to limit seed set. Despite this, the species sets few fruit. From examination of the taxonomic positions of likely buzz-pollinated taxa in the family, it appears that pollination by sonication has arisen independently several times in the Epacridaceae, with primarily two different floral configurations.