REPRODUCTIVE-BIOLOGY OF THE RARE AND ENDANGERED BANKSIA-BROWNII BAXTER EX R. BR. (PROTEACEAE)

Banksia brownii is an endangered species, now limited to similar to 15 disjunct populations in southwestern Western Australia. Data on flowe ring phenology, plant size, fruit set, pollination and the mating syst em were gathered for two of these populations between March and Octobe r 1993. Flowering for both populations followed a similar pattern, wit h open flowers first evident in April, and the number of inflorescence s with open flowers peaking in June. At both locations, trees differed considerably with respect to their size, the total number of inflores cences produced and the length of their flowering season. Fruiting suc cess was typically low, with approximately half of all inflorescences failing to develop into infructescences. Only 1.8% of the flowers orig inally present on inflorescences developed into follicles. The distrib ution of follicles along each infructescence was non-random, with most forming in the middle third of the infructescence for reasons relatin g to nutrient supply and pollinator behaviour. More flowers opened dur ing the day than at night, although pollen was lost from individual fl owers during both periods. Honeyeaters such as Phylidonyris novaeholla ndiae were common at the two study sites, and often carried large load s of B. brownii pollen. Though less frequently caught, the nocturnal m ammals Rattus fuscipes and Tarsipes rostratus also bore substantial am ounts of pollen. Most inflorescences from which these mammals and bird s were excluded remained barren. Fruiting success was further reduced when invertebrates such as Apis mellifera were also prevented from vis iting inflorescences. The ability of B. brownii to set at least some f ruit in the absence of biotic polinators indicates that the species is partially self-compatible. Honeyeaters foraged preferentially at infl orescences with one to two thirds of their flowers open, probing mainl y along the 'advancing front' of open flowers. These animals moved mor e frequently between inflorescences on the same plant than between tho se on different plants, and were often recaptured in the same location s. Mammals also appeared to be sedentary. Both B. brownii populations had mixed mating systems, with genetically determined outcrossing rate s of similar to 0.7. The unusually high level of selfing in each popul ation is presumably a reflection of the species' self-compatibility an d the foraging behaviour of its pollinators.