Australia isn't very good at political monuments. We have nothing to compare with the Lincoln Memorial, let alone Mount Rushmore. Our greatest leaders are seldom commemorated by more than a brass plate on the house where they were born, or, in the case of Harold Holt, the beach where he died (there's also that memorial swimming pool, of course). Even the doyen, Sir Robert Menzies, has to make do with an obelisk topped with a cement thistle in his birthplace, Jeparit, in outback Victoria. Irreverent locals call it Ming's Chamber-Pot.

All the more reason, then, to cherish those few solid memories we have - which goes at least some way towards explaining the paroxysm of outrage, even grief, that went around the country at the news that the 170-year-old ghost gum outside the railway station at Barcaldine, in western Queensland, had been hit with a lethal dose of the pesticide Roundup.

The tree is revered by the Australian Labor Party as its point of origin: according to the tradition it was here that striking shearers met in 1891, and when the strike was defeated met again with other unionists to endorse one of the shearers, Tommy Ryan, as the first official labour candidate to the Queensland colonial parliament. Until then it had been known as the Alleluia Tree, because it was here the local Salvos band gathered to play and proselytise; after the events of 1891 it was rechristened, rather pretentiously, the Tree of Knowledge.

It became a major place of pilgrimage for the ALP faithful. In 1991 Bob Hawke, as prime minister, planted a cloned seedling beside the old tree to mark the centenary of the strike. Sadly, the seedling also succumbed, although another clone, in the nearby heritage park, is thriving. This is a relief not only to the true believers but also to the citizens of Barcaldine, who took the attack on their foremost tourist attraction very personally.

"The only thing the poisoning hurt is the town itself," declares Marie O'Dell, who has worked in the Barcaldine Information Centre for more than a decade and written a historical pamphlet on the tree, "so there is no way a local would have done it." In fact, there are no real suspects, although the finger has been pointed at a gang of railway fettlers that has since left town. A reward of $10,000 has been offered for information, but nothing has been forthcoming.

The police admit they are baffled, and even Pat Ogden, the feisty publican at the Globe Hotel who has made the tree something of his life's obsession, has no real ideas. Although he is an old Labor man, he is inclined to think it was an act of mindless vandalism rather than a political attack; after all, as he points out, the tree was an icon that transcended party lines. When it has been in trouble in the past, from disease, caterpillars, white ants and constricted root-space, the town has rallied to save it. Tree surgeons have been called in from across the country, roadways have been dug up, and everything from hormones to creosote and plaster of Paris used to keep it going.

But this time, Mayor Rob Chandler admits, the damage looks terminal. The bare and twisted limbs give no sign of regrowth, even after repeated flushings of fresh water to leach the poison away. It appears that the Tree of Knowledge has gone to join the history it commemorates.

Or does it? Some pesky pedants, such as Associate Professor Bradley Bowden of Griffith University, say the local version is more myth than reality. There is no real argument about the background: in 1891, with the price of wool plummeting on the international market, the woolgrowers presented the shearers with a workplace agreement which drastically reduced their wages and conditions. The union directed the shearers not to sign, and the squatters dismissed them and tried to replace them with free labourers. Thus it was actually a lockout, but it became known as the Great Shearers' Strike.

The unionists attempted to block the strikebreakers, and to persuade them to back off; there were sporadic reports of assault and sabotage. The conservative politicians believed, or pretended to believe, that they were witnessing the lead-up to a full-blown socialist revolution, and had fourteen of the strike leaders arrested and charged with conspiracy. Thirteen were convicted and jailed on the island of St Helena, in Moreton Bay, the most hellish of the old convict prisons.

The strike/lockout was broken; the remaining union leaders met under the tree at Barcaldine, as they had during the conflict, and resolved to take their struggle to parliament. Tommy Ryan was nominated and elected on a labour ticket.

So far, so good; but Bradley Bowden finds that the historic record shows the Australian Labour Federation held its first meeting in Brisbane in 1890, the year before the strike, and the decision to form a political party was made then. Worse still, a Labour Party was already flourishing across the border in New South Wales, and it held a third of the seats in the Legislative Assembly in Sydney.

Unsurprisingly, Pat Ogden is not inclined to let the facts ruin the legend: "The meeting may have been held in Brisbane, but it was the policy of the Barcoo electorate - which was Blackall and Barcaldine - that they adopted to form the Labor Party, and that meeting was held under the Tree of Knowledge."

And there is no doubt that the story will live on, even if the tree does not. Who would want to commemorate the founding of a party in a backroom in Fortitude Valley - or, for that matter, in Canberra's Masonic Hall, the birthplace of the modern Liberals? The Tree of Knowledge is a great symbol for the Australian Labor Party; it remains as relevant as the Light on the Hill.

And, indeed, the times that it recalls may also be closer than we like to believe: John Howard's industrial-relations policy has disturbing overtones of the strike and its aftermath. Nearly sixty years after the event, Helen Palmer wrote ‘The Ballad of 1891'. The last verse is:

To trial at Rockhampton the fourteen men were brought.
The Judge had got his orders, the squatters owned the court;
But for every man was sentenced, a thousand won't forget:
When they jail a man for striking, it's a rich man's country yet.

Like the Tree of Knowledge, history produces its clones.