Mongarlowe mallee’s mysterious locations remain top secret as scientists attempt hand pollination
Four top-secret locations in the southern tablelands of New South Wales are home to Australia’s rarest tree species.
And, with just six individuals, the mysterious Mongarlowe mallee is perhaps Australia’s loneliest tree.
First discovered by a Braidwood landowner in 1985, the mysterious eucalyptus, also known as Ice Age Gum, is believed to be between 3,000 and 13,000 years old and is the rarest tree in the country.
A second plant was discovered in the Mongarlowe area in 1990 by a botanical consultant undertaking a vegetation survey in relation to the then proposed Welcome Reef dam, while a third plant was located north of Mongarlowe during a targeted aerial survey.
The critically endangered plants survive on private land in four secret locations on the southern tablelands, three near Mongarlowe and one near Windellama. Three of these sites each support only one plant, while the other site has three individuals.
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Department of Planning and Environment (DPE) scientists are working with Australia’s National Botanic Gardens with the aim of hand-pollinating plants to produce viable seeds and eventually grow ex-situ stock.
Mongarlowe’s mallee grows to 4.2 meters tall and has small, distinct, opposite, outward-curving leaves.
DPE’s senior ecologist, General Wright, said a closer look at the Mongarlowe mallee only raised more questions.
“This is a unique eucalyptus, and its survival in the wild depends on the last known adult plants – of which there are only six,” said Gen.
“We think these trees are very old and could be relics of past climates where they may have been more prevalent.”
Gen said that the flowering and seed production of the tree was very strange.
“Producing viable seed is difficult because the distance between all known trees is greater than any self-respecting pollinator would want to travel,” she said.
This means that the only pollen available to all Mongarlowe mallee trees is from its own flowers, which will not produce viable seed, or from other eucalyptus species that are flowering nearby at the same time.
Seeds produced with pollen from these neighboring trees yield hybrids, which is a eucalyptus that is a genetic mixture of two species and does not produce a true Mongarlowe mallee tree.
The only way to solve this problem is hand pollination, and in 2001/2002 the first viable seed was produced using this method. At the time, all the trees in Mongarlowe mallee were flowering at the same time, but in 2020 they were out of sync.
“Each plant now flowers at a slightly different time with just a short period of overlap, which makes repeating this cross-pollination extremely difficult,” Gen said.
“To complicate matters even more, some plants just don’t flower at all!
Conservation groups are focused on the long-term protection of these special trees and their habitat, as they are likely to live for at least another few hundred years.
Gen said all the trees are on private land, so it was extremely important to maintain a positive connection with the landowners, as they are the true guardians of the plants.
Their location is kept top secret, as a major threat to this botanical curiosity is increased visitation and collection of specimens by overly enthusiastic members of the public.
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It is hoped that future hand pollination will produce viable seeds. The Australian National Botanic Gardens in Canberra are ready to grow any seed and are also testing techniques for propagating the species using special grafting techniques.
Gen said all of this could lead to an ex-situ population of the plant, and it could one day become a garden plant like the Wollomi pine.
“We have so much to learn about this plant… how long do they take to grow and how old are they? Are they the oldest eucalyptus trees in Australia? Will we ever find another? she says.
A national recovery plan for the Mongarlowe mallee takes into account the conservation requirements of the species throughout its known range and identifies measures to be taken to ensure its long-term viability in the wild, including site protection , comprehensive genetic studies and the possible lowering of the maximum water level of the Windellama dam.