Main Club, 7 February 2025
Our speaker was botanist Dr Mark Brundrett, Adjunct Associate Professor at the University of Western Australia and a research associate at the WA Herbarium. He talked about the relationships between the shapes and colours of our wildflowers and the animals that pollinate them. This talk was based on his paper in the Australian Journal of Botany. His talk applies to the Southwest Australian Floristic Region (SWAFR) but holds true to some extent across Australia.
The SWAFR comprises a mosaic of different soil types and very high plant diversity, with about 8,000 species that are nearly all endemic to the region. These plants are very ecologically complex by world standards, with features to deal with fire, poor soils, drought, seed dispersal, and pollination.
Of course, plants that fail to pollinate will go extinct. Since plants outnumber pollinators, strong selective pressure exists to attract them, using colours, scents and shapes. Pollination strategies can be inferred by examining features such as corolla and pistil length, for which reliable data exists, and comparing this data with bird bill length. Plant-pollinator strategies were confirmed by actual observation of pollination activity. (Our Club has published a book listing animals that visit many wildflower species).
Grasses, sedges, rushes, Callitris, Sheoaks, and, surprisingly, Stirlingia latifolia are wind pollinated. Macrozamia reidleii, a Gymnosperm, is typical of wind-pollinated plants but is pollinated by Weevils attracted by pheromones. A third of our flora have general insect pollination. They usually have small, bright flowers, including Dasypogon, wattles, daisies and Geraldton Wax. These flowers attract bees, flies, butterflies, wasps, etc.
Mark showed us a wonderful video of a bee using buzz pollination on a Fringed Lily. Bees vibrate like a tuning fork, causing the anther to expel pollen. Other genera using buzz-pollination include Hibbertia, Dianella and Conostephium.
Big, red flowers are usually adapted for bird pollination since insects don’t notice red. In the SWAFR, 13% of plants are bird-pollinated, as against 5% globally. Birds fly further than insects, and this promotes cross-pollination. Among the family Proteaceae, the genera Adenanthos, Banksia, Grevillea and Hakea are mostly bird pollinated. Co-evolution is evident between pistil length in different flowers and bill size in bird species. Other Proteaceous genera use insects and a few use mammals. Dull-coloured, hidden flowers with a musty smell close to the ground attract mammals, such as the Honey Possum, Pygmy Possum, Dunnart and mouse (but not bats).
The pea family contains species with bee-pollinated flowers and highly modified, red, bird-pollinated flowers. Some other families do similarly.
Most orchids rely on trickery for pollination. Some mimic other flowers but don’t produce nectar. Insects visit a familiar-looking flower but leave without their reward. Other orchids use sexual deception, attracting male wasps or fungus gnats.
Mark showed us the evolutionary trends in pollination strategies in the SWAFR, from general insect pollination to the more specialized strategies he had discussed. He believes that the SWAFR is the most important place to study plant diversity and evolution and that it invites more research, especially in light of changes such as land clearing and climate change.
Mike Gregson