The unusual, closed flowers of Erica lanuginosa (Ericaceae) are adapted for rodent-pollination and not cleistogamy

Abstract

In the Cape flora, pollination by small mammals is well known in the Proteaceae and has recently been documented in the Ericaceae. Erica lanuginosa, a Klein River Mountains (southern Overberg) endemic, has unusual pendulous, acorn-shaped flowers unlike those of a typical Erica as the lobes of the corolla are tightly pressed together at the tips to form a sharp closed “beak”. These unusual floral traits suggested the possibility of autonomous self-pollination in flowers that don't open (cleistogamy) or rodent-pollination. We used digital camera traps, mammal trapping and pollinator exclusions to test these alternative hypotheses. We show that Erica lanuginosa, is pollinated by small mammals, the second documented rodent-pollinated Erica species. Camera traps recorded fourteen images of three species of rodents visiting flowers on seven separate days to three different plants, with the majority of visits by Acomys subspinosus. PVC Sherman-type traps were used to capture rodents and examine their scats for the presence of pollen. Pollen tetrads typical of Ericaceae were observed in droppings of all three species. Flowers of Erica lanuginosa covered with pollinator exclosure bags set no seeds while the proportion of open, control flowers that set seed was high, indicating that pollinators are essential for seed set in E. lanuginosa. These data are consistent with rodent-pollination in E. lanuginosa and there is no evidence for cleistogamy in this species.