Main Club 4 Feb 2022

Our speaker was botanist Mark Brundrett. Mark is Adjunct Associate Professor at UWA and Research Associate Professor at the WA Herbarium. He spoke about why the South West of WA is a biodiversity hotspot and why the flora is unique globally.

To be a hotspot, a region has to have high species richness and a high level of endemism, rarity and endangerment of species. The flora of the SWAFR (South West Australian Floristic Region) has all of these. These features are the result of our climate and soils. The plants have had to adapt to adverse conditions such as soils that are ancient and leached of nutrients, a hot, dry climate and frequent fire. We have about 8000 species, compared with less than 5000 in eastern Australia’s much larger floristic region. Most are not found anywhere else, and many are rare and endangered. Rarity is intrinsic to the flora, but increasing aridity, feral animals, weeds and land clearing increase that endangerment. In global terms, the SWAFR flora is quite special with regard to pollination, adaptation to fire, and nutrition.

1. Plants compete to be pollinated, using different colours, structures and placement of flowers. There are various pollination syndromes; some use wind (e.g. grasses and casuarinas). Some, with large, tough, red flowers, use birds (pollen presenters are particularly suitable for this.). Some, with dull, musty, hidden flowers, use mammals. Insect pollination is the most common. Some, with large, closed anthers, use buzz pollination. The peas are specialised for native bee pollination. Trigger plants use mechanical means. Some flowers use colour to show whether they have been pollinated. And then there are the orchids, which deceive insects in various ways into pollinating them.
   
2. Plants in the SWAFR show an unusually wide range of adaptations to fire. Some re-sprout from lignotubers or rhizomes, some store seed, either in the canopy or the soil, some drop seed after a fire, and some have a combination of strategies – for example, being able to re-sprout and re-seed. Some even depend on fire for seed dispersal or germination. Unfortunately, weeds gain massively after a fire.
   
3. A large proportion of SWAFR plants have highly specialised strategies for getting nutrients. Many have mycorrhizal associations – i.e. they are symbiotic with fungi that glean minerals in exchange for sugars. (Thysanotus has a unique type.) The Proteaceae have cluster roots to draw phosphates from the soil, and the legumes (peas and wattles) have bacteria on their roots to fix nitrogen. Moreover, several plant groups in the SWAFR are parasitic or semi-parasitic, and several are carnivorous.

Mark said that people involved in research on the SWAFR flora need to understand adaptations to all three factors – pollination, fire and nutrition – to manage threatened species and ecosystems. In a recently published paper, he said that the threats to the flora are increasing, especially with climate change, and that our region is the best location in the world to study the impacts of climate and soil on plant evolution and diversity.

Mike Gregson

Read More:

Brundrett M.C. 2021. One biodiversity hotspot to rule them all: Southwestern Australia — an extraordinary evolutionary centre for plant functional and taxonomic diversity. Journal of the Royal Society of Western Australia 94: 91-122.