Picture blue gum and you probably picture the florist's version: round silver-blue coins on a straight stem, the thing that goes in a vase or gets hung over a shower head. That is a young plant. A mature blue gum looks nothing like it, and understanding why is the fastest way into this tree.
Named twice for the same hat
A eucalyptus flower bud is sealed under a little cap, which pops off when the flower opens. The whole genus is named for it: Eucalyptus, from Greek roots meaning well covered. Then globulus, Latin for a little button, describes the shape of that same cap on this particular species. Genus and species, both pointing at the lid.
The tree itself is enormous. Thirty to fifty-five metres is ordinary, the tallest measured specimen in Tasmania stands over ninety, and there are nineteenth century claims of taller. Smooth bark peels away in long ribbons and leaves a pale surface behind. It was proclaimed the floral emblem of Tasmania in 1962.
Its range needs a bit of care, because Eucalyptus globulus is not one tidy population. Botanists recognise four subspecies scattered across Tasmania, Victoria and New South Wales, and they intergrade so freely where they meet that a specimen from southern Victoria can be impossible to assign. The one that carries the emblem, and the one planted and distilled around the world, is subspecies globulus, the Tasmanian blue gum proper. That subspecies is essentially a lowland Tasmanian tree, reaching the Bass Strait islands including King Island and holding a small footing on the Victorian coast. So the honest answer to where blue gum comes from is Tasmania, with an asterisk, and the asterisk is bigger than most labels admit. Twentieth century forestry plantings have muddled the natural boundaries further.
The blue does not last
Blue gum changes its leaves as it grows up, and the change is drastic. Juvenile leaves sit in opposite pairs, pressed straight onto square stems, broad and rounded and coated in a waxy blue-grey bloom. That bloom is where the name comes from. Adult leaves are a completely different object: alternate rather than paired, long and narrow and sickle-shaped, fifteen to thirty centimetres, glossy dark green, hanging vertically so the canopy casts surprisingly thin shade.
So the cut foliage trade sells juvenile growth, deliberately, because the blue phase is the pretty one and cutting the plant back keeps it in that phase. A blue gum left alone in southern Tasmania grows out of it within a few years and never goes back.
How an Australian tree became a global crop
The commercial story runs almost the whole length of the colonial period, and it is worth laying out in order.
- 1788. Ten months into the colony at Sydney, Surgeon-General John White sends roughly a litre of distilled eucalyptus leaf oil back to England. It was Eucalyptus piperita, not blue gum, and it has a fair claim to being the first useful thing Australia manufactured and exported.
- 1792. The French botanist Jacques Labillardiere collects the type material on the d'Entrecasteaux expedition. It is dated December of that year and most probably from Recherche Bay in southeastern Tasmania, though even the formal type citation hedges on the spot. Seed reaches Europe soon after.
- 1852. Joseph Bosisto, a Yorkshire-trained pharmacist prompted by the Victorian government botanist Ferdinand von Mueller, opens a crude still at Dandenong Creek. This is the start of the commercial industry, and the leaves going into it are a form of Eucalyptus radiata, not blue gum.
- 1858. The Victorian town of Kyneton lights its shops, hotels and houses with gas made from gum leaves, after an English engineer works out they can stand in for coal. The gasworks ran on leaves for roughly twenty years.
- 1880s. Blue gum enters commercial distillation properly, with Tasmanian farmers distilling it alongside the established species.
- By 1900. Australia is supplying the world with eucalyptus oil and remains the dominant producer well into the twentieth century.
- 1950s onward. Labour costs bite. Cheaper oil out of Spain and Portugal, and later much larger volumes out of Asia, undercut Australian production. The industry contracts hard and never regains the share it had.
Where the oil actually comes from now
Here is the part most listings skip. Blue gum dominates the global eucalyptus oil market today largely because it is the world's favourite pulpwood eucalypt. It grows fast and straight, so it is planted in enormous quantity overseas for paper, and the oil becomes an available by-product of that industry rather than the reason for planting.
Blue gum leads the world market because it is cheap and abundant, not because it was ever judged the finest eucalyptus oil. Those are different claims and they get quietly merged.
None of which makes it bad oil. It is the benchmark for a reason, it is rich in 1,8-cineole, and for steam inhalation or clearing a stuffy room it does exactly what people want from it. But if origin matters to you, and with eucalyptus it reasonably might, it is a fair question to ask of any bottle rather than assume that an Australian tree means an Australian still.
What it smells like, and where it sits
Sharp, camphorous, unmistakably medicinal, with that cold catch at the back of the nose that cineole gives. It is the smell most people mean when they say eucalyptus, which makes it the reference point rather than the interesting one. Among what I stock, radiata is the softer, sweeter, easier version of the same idea, and blue mallee is the harder, cleaner, more penetrating one. Blue gum sits in the middle and is the one to reach for when you want the effect everybody recognises.
Practical notes, since this is an oil people use rather than admire. Dilute it. Cineole-rich eucalyptus should be kept well away from the faces of babies and young children, and it is worth a word with a practitioner if asthma is in the picture. In a diffuser or a bowl of hot water it is close to unbeatable for the price.
What I like about blue gum is the awkwardness of it. It is the tree everyone can name, the emblem of a state, and a species that has been so successful abroad that its own country is now a minor supplier of its oil. That is a strange thing for a plant to have achieved, and it is worth knowing about the bottle on the shelf.