The World's Rarest Plant Has One Wild Individual Left in South Australia

Along the Coorong coastline in South Australia lies a forgettable stretch of road called Woods Well. Scattered houses, open paddocks, remnant scrub… nothing that would make a traveler slow down. 

Yet hidden in the roadside vegetation grows what may be the last wild specimen of one of the country's most critically endangered plants.

A Species on the Brink

The Woods Well spyridium is a small mallee shrub, reaching about 1.8 meters in height, with white flowers that offer few obvious clues to its identity. 

"It's a pretty hard plant to identify because it doesn't have any really distinctive features," says Dr Robbie Andrew of the Limestone Coast Landscape Board.

The species was first recorded at this roadside location in 1973, but wasn't formally described as a distinct species until 2012 — recognized as related to, yet different from, other rare spyridium varieties found on the Fleurieu Peninsula and Kangaroo Island. At the time of its scientific description, the population had already been declining for years due to land clearing and habitat fragmentation.

Today, only one plant is known to survive in the wild. It is growing in crushed limestone on the road verge, in a narrow strip stretching just 200-300 meters.

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Seeds Banked Before It Was Too Late

When ecologists first collected seeds from the roadside population in 2006, 35 plants were still alive. Those seeds were split between two institutions: half went to the SA Seed Conservation Center at the Adelaide Botanic Garden, and half were sent to the Millennium Seed Bank at Kew Gardens in London. That early decision now looks prescient.

An additional 3,000 seeds have been collected this year. Several plants are now growing in the botanic garden's seed orchard with other threatened South Australian species. But even under controlled conditions, germination has proven stubbornly difficult.

Why Won't It Grow?

The plant's reluctance to reproduce naturally is one of the central puzzles facing researchers. Scientists suspect that soil disturbance may be the key trigger for germination.

Also, the plant's life cycle compounds the problem. Unlike long-lived trees, Spyridium shrubs survive for decades, setting seed throughout their lives and relying on specific environmental cues to trigger germination. Confined to a small linear strip of roadside, the species has lost access to the natural processes that would normally sustain it.

The Hunt Continues

Targeted searches across nearby properties and conservation areas have so far found no additional wild populations. However, researchers believe there is a reasonable chance that viable seeds remain dormant in the soil near the surviving plant. Trials are planned to test whether controlled burning or deliberate ground disturbance could trigger natural germination.

Of the 45 known Spyridium species in Australia, this is among the rarest and the only one endemic to this particular corner of South Australia.