It was the botanical equivalent of finding dinosaurs alive, but now the Wollemi pine faces a new threat to its fragile existence.
In 1994 the world was stunned when David Noble, a park ranger on a holiday hike, stumbled upon a living population of conifers that before then had been seen only as fossils.
Botanists at the Royal Botanic Garden, including Cathy Offord, realised the plant was one believed to have been extinct, and which had a fossil record dating back 90 million years.
The Wollemi pine was reborn.
Now one of the four stands of the Wollemi pine in the Blue Mountains has developed a fungal disease, likely from unauthorised hikers carrying in the Phytophthora mould.
"It would only take one extreme event to push them to extinction," said Heidi Zimmer, a research biologist who has just completed her PhD at the University of Melbourne on the Wollemi pine.
The ancient population of Wollemi pines is missing middle-aged trees, which is also concerning botanists. There are fewer than 100 mature individuals in the wild and fewer than 300 juvenile plants.
"It's like getting to a community and there are a lot of retirees and toddlers," Dr Zimmer said.
The Wollemi pine was upgraded to critically endangered by the NSW Scientific Committee last year because it is so susceptible to Phytophthora cinnamomi, a pathogen which causes dieback of branches and stems, and because there are so few specimens left in the wild.
While no individual trees have died from it, there is no comprehensive control to treat it, although scientists are experimenting with injecting a fungicide into infected trees.
The listing recognises that the Wollemi pine faces an extremely high risk of extinction in NSW in the immediate future.
In 2012, Dr Zimmer, Dr Offord and their colleagues planted a grove of trees in a new location to see how well the species coped with being moved, in a process botanists call translocation.
They planted 191 trees at 30 sites with varying degrees of light and moisture. Of those, 29 died, most due to infection from Botryosphaeria fungi. These were largely in damper and darker locations.
Most of the others are thriving, and are giving botanists valuable information about the best conditions for them to grow. "They're doing much better in the higher, light sites," Dr Zimmer said.
The next step will be to establish bigger populations in national parks, choosing cooler sites which are predicted to remain within the Wollemi pine's known temperature tolerance range (-10 to 35C) for the next 100 years.
