Horehound (Marrubium vulgare), a Eurasian medicinal herb and ubiquitous inland nuisance of grazed land and roadside throughout SE Australia. Unpalatable to sheep, with seed cases adapted to hitchhike upon wool or clothing, countless generations of selective pressure in the Northern Hemisphere prepared this member of the mint family to make the jump to Australia following the continent’s depletion and conversion to dubious grazing land by the British.
Horehound was ‘everywhere by the roadside’ at George Town in Tasmania by 1855, and had naturalised at Paramatta by the time it was mentioned in an 1857 column in the Sydney Morning Herald. Although its introduction has been attributed to domestic use as a cough medicine, Horehound may very well have been arriving simultaneously as a wool contaminant. Digital records of the first clearly naturalised collection place it in 1853 Melbourne, on the banks of the Yarra adjacent to the Port Fairy and Warnambool ferry docks.
The plant was also introduced intentionally to sheep stations; an 1869 writer to the Queenslander spruiked one weed as antidote to another: ‘SIR: It is an ascertained fact that where the horehound grows upon old sheep folds the Bathurst burr becomes extinct… I can point to many old sheep stations where the burr pest has been quite destroyed by the encouragement of horehound.’
A note in a 1929 copy of The Australasian suggests another obscure source of introductions, recounting that ‘all that remains of the Sir John Franklin [a hotel on the Mount Alexander Road near Keilor] is probably the usual patch of horehound which for long years afterwards was the last sign left by hotels and shanties that had long disappeared. The explanation was that the soft horehound was the packing generally used in cases of bottled beer shipped from England.’
Although still popular as a medicinal, the species was glossed over by von Mueller in his 1860s-70s acclimatisation advocacy, not for its inutility but because it had ‘already copiously naturalised here’.