Large Mediterranean Spurge (Euphorbia characias), another beloved Eurasian garden filler with gloriously alien inflorescences and caustic latex sap.
Tolerant of drought and high salinity levels, cultivars of the species were adopted into the Australian horticultural flora beginning in the 1920s and 1930s, and quickly became a favoured selection of designers and garden columnists here.
This spurge appears from online records to be established as an occasional naturalised plant in parts of Northern Europe and the UK, and in New Zealand. A ‘notorious self-seeder’ according to online accounts from the UK, it has yet to demonstrate the same capabilities here in Australia, or in the superficially similar climate of California; in both cases it has not moved beyond the status of casual adventive around the edges of domestic gardens and tip sites.
The Flora of Victoria does not treat Euphorbia characias as truly naturalised here. Adventive colonies persisting from dumped garden waste have previously been recorded at Williamstown and Brimbank. There have also been a pair of similar garden escapes recorded from Tasmania.
Euphorbia characias may be dependent on a particular pollination schema that has not been addressed here; perhaps the local drone flies do not visit it effectively? It is also possible that there is an incompatibility with its explosively released seeds. For instance, the seeds, which are not persistent, may only rarely be viable long enough to experience favourable moisture and climate conditions for germination. Leave a comment of course if you have experiences with E. characias volunteers in your own gardens.
The photographed sprays are established on broke pavement in a Richmond alley at the edge of the Jolimont railway cuttings, and at the foot of the Flinders Street railway embankment (in two clumps). Neither instance is likely to spread in any damaging way from such positions, however they may be of value in assessing whether the species can overcome its limitations here.