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

Abstract

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.

Flower morphology of the resurrection plant Chamaegigas intrepidus Dinter and some of its potential pollinators

“…Thus, endemic species may be preferentially cross-pollinated under ideal conditions of pollinator visitation, but can revert to self-pollination in the event of outcross failure (e.g. Brachycome muelleri, Jusaitis et al, 2003). For Agalinis neoscotica (Scrophulariaceae) precocious self-pollination in buds was found, assuring reproduction in the absence of pollinators (Stewart et al, 1996).…”

Seed dormancy in Asteraceae: a global vegetation zone and taxonomic/phylogenetic assessment

“…However, the presence of cypselae in the soil tells us very little about how long they can live after burial. Studies of individual species of Asteraceae that involved collecting soil samples at population sites and counting the number of viable cypselae in the sample or the number of seedlings that emerged from them have been conducted for various species, for example, Ageratina adenophora (Shen et al, 2006), Artemisia quettensis (Ahmad et al, 2007), Brachyscome muelleri (Jusaitis et al, 2003), Centaurea solstitialis (Joley et al, 2003), Chromolaena odorata (Epp, 1987;Witkowski and Wilson, 2001), Pilosella aurantiaca, P. piloselloides subsp. praealta (Bear et al, 2012), Polymnia canadensis (Bender et al, 2003) and Symphyotrichum laurentianum (Kemp and Lacroix, 2004).…”