Reproductive biology of a threatened Australian saltmarsh plant – Wilsonia backhousei

The reproductive biology of a threatened saltmarsh plant, Wilsonia backhousei Hook.f., was investigated with a view to improving conservation and restoration outcomes for the species. Population phenology was studied every two weeks, over two consecutive flowering seasons, in three to six 0.25 m2 quadrats set in monocultures of the species at each of eight sites in New South Wales, Australia. Floral density (flowers m−2) ranged from 0 to 5800 ± 1400 m−2 and varied significantly among sites (P < 0.05). Peak flowering occurred in mid-late October, during a period of no tidal inundation; fruit maturation coincided with inundation by extreme high tides in December, January and February. Sediment samples collected from each quadrat post-flowering were analysed for water content, salinity, texture (clay content) and pH. Ordinal logistic regression (OLR) of floral density against foliage volume and sediment variables showed a significant positive response to increasing foliage volume and negative responses to increasing salinity and clay content (P < 0.05). Foliage volume, in turn, showed a significant positive response to sediment water content and again negative responses to increasing salinity and clay content (P < 0.05). Fruit development occurred at all sites; however, little to no seed was produced at five of the sites. When quadrats not producing seed were excluded (to limit the influence of self-incompatibility), OLR of seed yield against floral density and sediment variables indicated sediment water content was the only significant predictor of yield (P = 0.015). The morphology and phenology of individual flowers, potential pollination vectors, and general seed biology were also investigated. A combination of floral characteristics indicated that W. backhousei is wind-pollinated, likely to be outbreeding, and may be self-incompatible. The fruit is buoyant and, as maturation coincides with inundation by extreme high tides, may be dispersed within and among sites by tidal flow. The seed was found to be viable and long-lived (>70% germination in both fresh seed and seed aged for 6 years); however, seed germination is limited by physical dormancy and is significantly reduced by salinity levels ≥40 dS m−1 (6 ± 2.4% after 28 days, P < 0.001). Based on these outcomes, recommendations are made for maximising the reproductive potential of remnant and restored populations.

► Wilsonia backhousei is chiefly wind-pollinated.
► Reproductive potential is strongly influenced by sediment water content.
► The fruit is buoyant and may be dispersed by extreme high tides.
► The seed is viable and long-lived.
► Germination is inhibited by physical dormancy and saline substrates.