Population structure, flowering and seed production in the endangered Whibley Wattle, Acacia whibleyana (Leguminosae: Mimosoideae)

Acacia whibleyana (Whibley wattle) is a nationally endangered wattle, endemic to the near-coastal region around Tumby Bay on the Eyre Peninsula in South Australia. Two distinct sub-populations, referred to as the Quarry and the Salt-lake populations, each contained plants growing on roadsides and in scrub fragments. Marked differences were observed in the population size structure between the two populations. The absence of juveniles on roadsides in both populations signaled potential limitations to natural recruitment. Studies of reproductive biology of scrub plants over two years (1996-1997) indicated that between 1.1% (Salt-lake) and 6.9% (Quarry) of A. whibleyana inflorescences produced fruit. Each infructescence produced an average of 1.2–1.8 pods, although up to 10 pods per infructescence were observed at the Quarry scrub in 1996. Each pod contained 4–6 seed on average, with a viability of 85%. Plants at the Salt-lake scrub generally set less fruit, produced fewer pods per infructescence, and had lower seed numbers per pod when compared with Quarry plants, differences attributable to the superior vigor of Quarry plants. A. whibleyana seeds were dispersed by ants attracted by the lipid-rich aril. The soil seed bank had a patchy distribution across both sites possibly due to seed concentrating in the vicinity of ant nests. We concluded that the reproductive attributes studied were unlikely to constrain natural recruitment of A. whibleyana as both populations were capable of producing viable seed over the two years of this study.Manfred Jusaitis, Birgitte Sorensen and Lesley Polomk

Reproductive biology of the endangered Brachycome muelleri (Asteraceae), an endemic herb of Eyre Peninsula, South Australia

The reproductive biology of Brachycome muelleri Sonder (Asteraceae) was studied from 1995 to 1997 by using nursery and field experiments. Reproductive development and seed dispersal occupied approximately half of the 4-month growth cycle. Flowers of B. muelleri did not have any obvious self-incompatibility systems and were readily selfed to produce viable seed. It appeared that B. muelleri may be preferentially cross-pollinated under ideal conditions of pollinator visitation, but could revert to self-pollination in the event of outcross failure. Seed dispersal was assisted by the epinastic curvature of peduncles as fruit matured, bringing capitula into contact with the soil a short distance away from the parent plant. Slight wind-stimulated movement of the capitulum was sufficient to dislodge seed directly onto the soil surface. Seed was shed in the immediate vicinity of parent plants and although some short-range movement facilitated by rain splash, water flow and gravity was observed, no long-distance dispersal mechanisms were apparent. Annual seed production of the single extant population of B. muelleri in South Australia was estimated at about 5 million seeds. Immediately after dispersal, the soil seed bank in the vicinity of B. muelleri plants contained, on average, over 1700 germinable seeds m–2. Many of these seeds germinated or died within a year, the remainder persisting into a second or third year. Seed viability under field-burial conditions declined to less than 10% over that time. Population size did not appear to be limited by seed production, but rather by seed dispersal syndrome.Manfred Jusaitis, Birgitte Sorensen and Lesley Polomk

Habitat specificity, seed germination and experimental translocation of the endangered herb Brachycome muelleri (Asteraceae)

Brachycome muelleri Sonder (Corunna daisy) is an endangered annual herb, endemic to the upper Eyre Peninsula of South Australia. It is restricted to a single population occupying an area of approximately 3 ha on steep, south-facing cliff-foot slopes of the Baxter Hills. Its unique habitat, within an otherwise generally arid region, optimises soil moisture retention through the provision of concentrated water catchment, shade, and low evaporation rates during the growing season. Weeds had the potential to significantly disrupt recruitment, growth and reproductive output, but grazing did not constitute a direct threat to the population. Fresh seeds were innately dormant, requiring a period of after-ripening before they would germinate. Dormancy was artificially broken by gibberellic acid (GA3) treatment. Germination was optimal at 20°C, and it was proposed that temperature plays an important role in regulating germination in situ. B. muelleri seeds did not respond to smoked water treatment, and GA3 (1000 mg l-1) was recommended as a routine seed treatment to stimulate germination. Trial translocations using seed as founder propagules resulted in low establishment, growth and flowering rates. Established seedlings provided several advantages over seed as founder propagules, including higher success rates, more vigorous growth, and improved seed yields in the first season. Successful regeneration, proliferation and expansion of a new translocated population was observed and recorded over four consecutive years. We suggest that conservation management of this species should include the establishment of several new populations by translocation to suitable, isolated, weed-free sites. © 2003 Elsevier Ltd. All rights reserved.Manfred Jusaitis, Lesley Polomka and Birgitte Sorense