I will start where you might not expect me to start: a long time ago. Nothing in the natural world can be understood except in the light of evolution. For our native plants, we need to understand the effects that changing climatic and soil conditions could have had on the plants of those parts of Gondwana that were to become Australia.
Before 45 million years ago, when we were part of Gondwana, there was no gap between us or South America and Antarctica, so there was no circumpolar ocean circulation. The climate of Australia was subtropical and wet. Rainforest dominated the land. For millions of years, soils were constantly leached. This leaching gradually removed much of the phosphorus that had been in the volcanic rocks from which the soils had been formed.
Then we started to separate from Antarctica and head north. Over the next tens of millions of years, Australia gradually became drier. The plants had to adapt to lower rainfall, a more seasonal rainfall pattern and its increasingly erratic year-to-year variation. Fires caused by lightening added a further evolutionary pressure. Evolve, or perish!
In broad terms, Gondwanan plants had to adapt to low phosphorus supply, frequent drought, high summer temperatures, and fire. They had to develop ways of extracting phosphorus from soils that had little. Their leaves had to be able to survive drought: they became smaller, thicker and harder. To survive fire, they had to either develop seed capsules that protected their seeds until the fire had passed or they had to develop stem/trunk covers (bark) that resisted fire, plus the ability to grow again from epicormic buds.