Most rare materials are rare for a reason you can point at: a short season, a low yield, a difficult extraction. Boronia has all three, and it also has something less obvious. It is a plant with a specification, and the specification rules out most of the planet before you have even thought about farming it.
The list of demands
A cold winter, or no flowers at all
This is the one that decides everything. Brown boronia needs a genuine cool period to initiate flowering. Without enough winter chill the plant will happily grow leaves and simply never bloom, and since the flowers are the entire crop, a boronia that does not flower is firewood. That single requirement eliminates every warm-winter region on Earth, which is most of the places you might otherwise plant a fragrance crop.
Sandy, acidic, and desperately poor
It evolved on the ancient, leached soils of south-western Australia, which are among the most nutrient-starved on the continent. It is adapted to that, not merely tolerant of it. Feed it a normal fertiliser and the phosphorus damages the root system. The soil has to be free-draining and slightly acidic, sandy or gravelly, and hungry.
Moist, but never wet
More boronia is killed by waterlogging than by anything else. It wants consistent moisture and perfect drainage at the same time, which in practice means a specific kind of ground rather than a specific rainfall figure. It is also susceptible to Phytophthora, the root-rot fungus, so wet feet are not just a setback but usually fatal.
Shelter, and no hot dry wind
It grows naturally in dappled light at the edges of forest rather than out in the open, and hot dry summer wind will kill an established plant quickly. Full sun and exposure are both out.
And it will die anyway
Even given everything it asks for, brown boronia is short-lived. A few years is a normal span. Commercial growing therefore means continuously replacing plants, and since the species is stubborn from seed, with a thick coat and real dormancy, most propagation is from cuttings. Every plantation is a rolling programme rather than an orchard you put in once.
Which is why the map has two pins
The native range is genuinely small. Brown boronia grows from roughly Perth south to Albany and no more than about 150 kilometres inland, on low-lying seasonally wet ground, through the karri forests and along the southern margins of the jarrah between Harvey and Cape Riche. That is the whole natural distribution of a plant the world's perfumers depend on.
Western Australia is therefore the first pin, and it is where the plant belongs, where it is grown, and where the boronia I carry comes from.
Tasmania is the second. It is not native there, but it satisfies the specification: cold enough winters to set flower reliably, cool summers, the right soils in the right districts. It has been farmed as a fragrance crop there for decades, with a long-running agronomy partnership at the University of Tasmania working on yield and consistency, and a large share of the world's supply now comes from it.
Between those two, that is effectively all of it.
Why not somewhere easier
People have tried. Boronia is widely sold as a garden plant across Australia and it fails almost everywhere warm. North of the New South Wales and Victorian border, on the humid subtropical east coast, it can be kept alive for a season or two and is then treated as an annual to be replaced. That is a fine outcome for a pot on a balcony and a hopeless one for a crop.
Boronia is not scarce because someone is restricting it. It is scarce because the number of places that satisfy all of its conditions at once is, roughly, two.
The wild-picking question
One nuance worth being straight about. The species itself is not currently assessed as at risk in the wild, so this is not an endangered plant story. But brown boronia is also a significant cut flower crop, not only an oil crop, and over-cropping of natural stands in south-western Australia for the wildflower trade has prompted a genuine re-examination of harvesting practice.
The oil side sits apart from that. Commercial boronia absolute comes from managed plantations, which is the only way a material this demanding could be supplied consistently at all. But it is a useful reminder that "where does it grow" and "how was this particular batch obtained" are two different questions, and only the second one is really about your bottle.
For the economics of the absolute itself, the adulteration problem, and what the material actually smells like, there is a separate note on brown boronia in Australian Natives.