Bigleaf Hydrangea (Hydrangea macrophylla), the colour-changing Asian horticultural superstar, naturalised in damp forest situations around the world.
While North American species were already known to growers, this ‘horse of a different colour’ proved spectacularly successful when introduced to 1780s England through collections by Joseph Banks. While an 1826 columnist at Hobart could complain that Hydrangeas had yet to be brought to the colony, this was quickly rectified; by the 1830s the plants were being exhibited in both Sydney and TAS, and by the 1850s they were represented in growers’ catalogues at Melbourne.
Horticultural varieties have been bred to maximise the number of showy sterile flowers the plants produce; formation of fertile corollas and seed remains possible, however it is the canes which are usually key to their spread into native forest. By vegetative layering and rooting, Bigleaf Hydrangea is able to move down and across slopes and to raft to new sites along creeks and streams.
In NZ the plant was recognised as naturalised in the 1970s. In Australia, the first documented collection of Bigleaf Hydrangea outside of a cultivated context occurred in 1999 from roadsides in cool temperate rainforest in northern NSW. Further observations were made in the early 2000s in Sydney’s northern and western suburbs, but I can’t tell you more about those records as key location notes are scrubbed from the public version of NSW’s BioNet Atlas as a blanket policy.
In Victoria, the first collections of naturalised plants were made just after Christmas 2003. The collector, notable weed ecologist and taxonomist John Hosking of the University of New England, described the plants as ‘locally abundant’ at sites along Olinda Creek below Kalorama. Further records from the Dandenong Ranges followed: along Sassafras Creek in 2005, Emerald Creek in 2009, and in recent years around Tremont, Doongala and Ti-Tree Creek, as well as on Cement Creek near Warburton.
Plants have also recently been recorded in similar contexts in WA, QLD and Tasmania.