The curious reduction in the number of water-carrying cells toward the base of the branches in Wollemi pines may be part of the reason for their decline, according to an Australian botanist.
Credit: Charles Sturt University
SYDNEY: The system of water movement in the primitive Wollemi pine is one of a kind, and may be the reason for the species’ decline, according to a new Australian study.
According to author Geoff Burrows of Charles Sturt University in Wagga Wagga, New South Wales (NSW), the Wollemi has a remarkable reduction in the number of water conducting cells towards the base of each branch. “It is like connecting a drinking straw to your outside tap, then attaching your normal garden hose to the straw – the straw limits the flow of water from the tap to the hose,” he explained.
The small number of water conducting cells means that the tree’s branches are only loosely connected to the trunk, said Burrows, and may explain why the Wollemi cleanly drops whole branches at the trunk with leaves still attached, rather than dropping individual leaves like all other trees.
The ancient Wollemi is found only in a remote pocket of the Blue Mountains, near Sydney. It is believed to be the only tree species in the world to produce branches that never branch again - “like a ruler with leaves on it,” according to Burrows.
Burrows explained that the Wollemi’s branch-dropping mechanism may have worked well in the environment of 60 to 80 million years ago, when Australia was warm and moist with high levels of carbon dioxide. However, as the continent became hotter and drier, the design feature may have created problems for the plant by making it difficult to compete with newer species such as eucalypts that have much stronger water supply structures and are much better adapted to dry conditions.
“This unusual feature could be associated with the natural decline of the pine as the continent dried out,” Burrows said. “However it makes the Wollemi pine an even more interesting species to investigate, conserve and own, now that plants are available to purchase.”
The Wollemi Pine was discovered in 1994 by a NSW National Parks and Wildlife officer in an isolated gully in the Blue Mountains. Only a few of the trees have been found in the gully, although fossil records show the species was once widespread and abundant.
Burrows worked with trees produced from seeds supplied by the Mount Annan Botanic Garden, near Sydney. His findings will be published in the 99th edition of the Annals of Botany.
