Intuition says that where there are many flowers there is good soil. Almost everywhere that holds. Not here: the worse the soil, the more different species turn up.
And that contradiction is the key to understanding the landscape you will travel through, which at first sight looks like dry, unremarkable scrub.
01 Old, leached sand
The substrate of this region is a coastal plain twenty to a hundred and twenty kilometres wide rising towards gently undulating uplands, made of deeply weathered granite, gneiss and laterite.
The important word there is weathered. In a territory that has gone thousands of millions of years without new mountains lifting it or glaciers scraping it, rain has had all the time in the world to wash nutrients downwards and out to sea.
The result is sandy, acid soils with very little phosphorus, which is precisely the nutrient hardest to replace. In agricultural terms, this is bad land. In evolutionary terms, it is a laboratory.
Nothing has renewed this soil in aeons. That is why it is exhausted, and that is why it is full of rare species.
02 Why poverty multiplies species
The mechanism is counterintuitive but simple. In rich soil, a few vigorous species grow fast, shade out the rest and end up dominating everything: plenty of biomass and little variety.
In poor soil nobody can grow fast, so nobody dominates. Each plant survives by specialising in a minuscule niche: one particular kind of sand, one rooting depth, one pollinator, one position on the slope.
Multiplied by millions of years of isolation, that process produces what is here: an enormous number of species, many with tiny ranges, sometimes a few hills. It is the same phenomenon as the South African fynbos or the chaparral.
03 The banksias and their family
The family that best represents this region is the Proteaceae, which is also that of the South African proteas. Here their most visible member are the banksias, with those brush- or cylinder-shaped heads that look like a single flower and are hundreds.
Their adaptation to poor soil is one of the most elegant there is: they develop roots grouped into dense clusters that act as a capture network, releasing compounds that dissolve the phosphorus the soil holds tightly.
That detail has a practical consequence for the traveller and for anyone buying seed: these are plants so tuned to scarcity that, put in ordinary fertilised garden soil, they die. They cannot tolerate abundance.
04 Plants that eat insects
The most conclusive proof of how poor this soil is that there are plants here that have given up extracting nutrients from the ground and get them by hunting instead. The region holds over half the world's sundew species.
And they are not alone. There are also endemic carnivorous genera, plants that trap insects with tiny bladders in waterlogged ground and others that glue them with mucilage-covered leaves. It is a concentration of carnivorous strategies hard to match.
It is worth reading it in that order, because it is the order that explains everything else. These are not exotic plants by whim: they are the logical answer to a soil that yields neither phosphorus nor nitrogen, in a place that does have insects.
05 An island surrounded by desert
One ingredient is missing to complete the explanation: isolation. This region does not border another humid region, but deserts and arid shrublands that occupy the centre of the continent.
That turns the southwest into a biological island. The species that evolved here could neither spread out nor receive competition from outside, and they have spent millions of years cooking in their own pot, under a stable Mediterranean climate.
The less pleasant consequence is that the same isolation makes them fragile. A species that lives only on a handful of hills has nowhere to go if those hills change, and that is why the region appears on the world's priority conservation lists.
06 What to look for
First, crouch down. Most of what is interesting is under thirty centimetres tall and goes unnoticed from a car or even standing up. The local orchids, the carnivorous plants and much of the rare flora are at ground level.
Second, look at the ground when you move on. A change from white sand to yellow sand or to lateritic gravel usually brings a complete change of species within a few metres. That is the fine grain of the phenomenon.
And third, pick nothing and clean your boots. In a flora of minuscule endemics, carrying seeds or spores from one place to another is no small matter, and some areas have hygiene protocols for exactly that reason.
