Developmental evidence for stamen number reductionin populations of Hibbertia fasciculata (Dilleniaceae)

Abstract

Discrete Australian populations of Hibbertia fasciculata R. Br. ex DC. differ in stamen number per flower: three to four in isolated, northeastern coastal populations in New South Wales vs. 10–12 in southeastern Australian populations. In all populations, the stamen bases are attached to three broad flat pedestals regardless of number of stamens present. In certain other Hibbertia species, each pedestal results from initiation via a common stamen primordium that usually produces at least 3–4 stamens per common primordium. In H. fasciculata, each of the three pedestals is associated with three to four stamens in flowers of southeastern populations, but with only one stamen per pedestal in the coastal populations of New South Wales. Because the pedestals (remnants of common primordia) have persisted, the evolutionary trend probably has been one of reduction in stamen number. General observations and comparative studies suggest that this population-based reduction series in stamen number (as well as reduced plant size and flower size) reflects a locally successful trend towards smaller organs throughout the plant body together with a shift in pollination ecology.