Balkan Spurge (Euphorbia oblongata), a relatively common nursery distribution originating in Greece, which has naturalised in California, Britain and the low countries, and here in southeastern Australia.
Apparently not all Balkan Spurge comes with the flashy lime green bracts that help the nurseries sell you a plant full of caustic and inflammatory milk. Plenty of the weedy Californian material that is all over iNaturalist looks exactly like these plants, with nearly undifferentiated basic green bracts. On that basis, we will risk my limited credibility as an untrained interpreter of invasive botany and call this plant with the weird tuberculous seed pods Balkan Spurge, captured literally crawling under the proverbial garden gate of a Northcote terrace house.
Balkan Spurge was first recorded naturalised in New South Wales in the 1950s, where collections records from the gardens’ own herbarium tell the story of its insinuating spread, from an initial beachhead in the propagating depot, to the gardens’ dirt paths and thence into various collections beds. The species presumably escaped independently from other nurseries and private gardens throughout NSW and the ACT, to the extent that it is now an uncommon but broadly distributed weed of roadside, paddock and forest there. In Melbourne, Balkan Spurge was recorded repeating its botanical garden exploits at RBG-Melbourne in 2012, but in fact has been collected on what appears to be an increasing basis in Victoria since 2003.
The species’ readiness to produce viable seed in the Australian context, with at least some distribution potential from its explosive pods and perhaps an animal assistant, means that Balkan Spurge is likely moving from being a casual, local legacy of bad gardening decisions (as seen here) to being another novel environmental agent.