Floral biology, pollination vectors and breeding system of Zieria granulata (Rutaceae), an endangered shrub endemic to eastern Australia

Abstract

Context Understanding the factors that influence viable-seed production is crucial in the conservation of threatened plant species, yet these factors are often poorly understood. Aims We investigated the reproductive biology of Zieria granulata C.Moore ex Benth., an endangered Australian endemic with a limited distribution, with the intent of improving conservation and restoration outcomes. Methods Components of floral biology, including floral ontogeny and nectar production, were quantified to determine the pollination syndrome and the likely breeding system. Flower-visitor surveys (using both digital video recordings and human observations), a manipulative wind-pollination experiment and hand-pollination experiments were conducted to investigate pollination vectors and confirm the breeding system. Key results Z. granulata flowers were small, white, protandrous and produced highly ornamented pollen grains and small quantities of nectar; these characteristics suggest that the species fits the general entomophily syndrome. All floral visitors were arthropod species and of the 72 visitors observed, predominantly from the Dipteran and Hymenopteran families, 18 could be regarded as potential pollinators. Failure of simulated wind gusts (40 km h−1) to transport pollen ≥5 cm indicated that anemophily is unlikely for this species. Autonomous and manipulative selfing did not result in viable seed set, indicating that this is an obligate outcrossing species. However, fruit and viable-seed production was highly variable within and among some other treatments. Pre-dispersal seed predation was recorded at all study sites. Conclusions Pre-dispersal seed predation was recorded at all study sites and is a likely factor inhibiting viable-seed production. Implications This knowledge will be used to improve seed yield for collections used for ex situ conservation and restoration programs for the endangered Z. granulata.