Bringing an ancient mallee back from the brink of extinction
Gum trees that were widespread during the last ice age are being grown at the Australian National Botanic Gardens (ANBG), as scientists work to save the critically endangered species.
Eucalyptus recurva is a small, multi-stemmed tree, commonly known as Mongarlowe mallee or “ice-age gum”.
Just 6 extremely old plants remain in the wild in a small area of southern New South Wales and threatened species scientists believe they are at least 1000 years old.
The survival of these 6 trees is a key commitment of the NSW Government Saving our Species program, in partnership with ANBG.
Being widely separated from each other and flowering infrequently and at different times, natural cross-pollination is extremely unlikely.
Currently, the only known way to produce viable seed is through hand cross-pollination.
In December 2022, a hand-pollination project conducted as part of the Saving Our Species program resulted in the production of seeds on a single plant.
Twelve months later, ANBG nursery staff successfully sowed and raised 41 viable seedlings from this cross-pollination effort.
ANBG Conservation Horticulture Manager, Dr Veronica Briceno-Rodriguez says with so few wild plants remaining, E. recurva is experiencing an extreme genetic and demographic bottleneck.
“The seedlings we have successfully raised from hand-pollination represent a critical genetic bridge between the remaining wild plants, giving us the opportunity to potentially increase the current genetic diversity and strengthen the species’ long-term resilience,” she said.
“The work we are doing in close collaboration with the Saving Our Species program is creating the foundation for future reintroductions of this ancient species into its native habitat.”
This project builds on a grafting trial undertaken by the ANBG over several years as part of a previous propagation program to conserve E. recurva.
As a result, a number of ‘clones’ of 4 of the 6 wild plants are now held at the Gardens, and efforts are underway to successfully graft the other two.
A conservation seed orchard will be established in future at the ANBG using grafts from all 6 known wild individuals. This will allow for close monitoring of the plants as they grow, the collection of pollen from any individuals that flower and targeted hand-pollination work.
The aim is to produce seed that is as genetically diverse as possible, forming the basis of longer-term conservation efforts.
None of the plants at ANBG has yet produced seed. E. recurva is very slow growing, and the exact age at which it reaches maturity is not yet clear – it took the only known grafted plant 16 years to reach maturity.
Trials are currently underway at ANBG to assess whether the application of a plant growth regulator to the grafted plants can result in the stimulation of earlier and more prolific flowering and seed production.
Additional trials are also being conducted to assess the effectiveness and safety of the application of phosphite to E. recurva, as this chemical may provide plants with a degree of protection from the soil pathogen Phytophthora cinnamomi, which is known to occur in the landscape where this species is found.
