NZ’s rarest tree back from the brink
In mid-April 2010, Department of Conservation (DoC) workers planted some 1,600 seeds from what was once listed in the Guinness Book of Records as the world's rarest tree, Pennantia baylisiana.
Discovery of Pennantia baylisiana in 1945
By the mid-20th century, goats on Three Kings Island, off the northern tip of the North Island, had eaten the tree to near extinction. One remaining female specimen was discovered in 1945 by the late Professor Geoff Baylis. The tree was near the highest point of the island down a scree of boulders about 200m above the sea and too difficult for the wild goat population to get to. However, without a male tree for pollination to produce seeds, the species seemed doomed to extinction.
Professor Baylis describes the tree as at first looking a bit like a karaka. “I was soon gazing upon it in disbelief… this was no karaka. Its leaves were larger and recurved strongly in the sun, its bunches of small green flowers sprang from the bare branches below the leaves and there were no big berries – indeed, none at all.”
Professor Baylis wrote about his experience of finding the last surviving Pennantia baylisiana tree in the world in the Journal of the Royal New Zealand Institute of Horticulture (Vol. 2, No. 1, March 1997, pp. 12–13):
“Propagating this lone and sterile tree, not in the best of health because of insect damage, seemed urgent. There was a detachable shoot at its base, which took root in a damp sheltered place in my Dunedin garden and is now very like its parent with four slender trunks. But its canopy trimmed by occasional frost rather than repeated salty gales is taller (7m).
“While I was unsure that this shoot had really rooted, I was worried by failure both at the Plant Diseases Division at Mt Albert and at Duncan and Davies, New Plymouth, to strike cuttings from the crown. I asked George Smith, the chief propagator at New Plymouth, what I might do to provide better cuttings. ‘Cut the tree down,’ he said, and while I shuddered at the thought, he explained that he was confident about rooting shoots from the stump. But would there be any? Well, the tree had four trunks so I dared to sever one. A year later, the shoots were there. The naval launch on which I was a guest gave them a quick passage to New Plymouth, which happened to be its next port, and Mr Smith soon placed the survival of [the tree] beyond doubt.”
Cultivation of self-fertile seedlings
It took some 20 years for a viable population of cuttings to grow and for the plants to be established in cultivation. However, these cuttings were identical to their parent – predominantly female.
However, with advances in research, in 1985, Dr Ross Beever at Landcare Research, Mt Albert, managed to induce the latent pollen within the flower to fertilise itself by selectively treating them with plant hormones. One of the resultant seedlings, dubbed ‘Martha’ as in ‘Arthur or Martha’, has proved to be self-fertile, and in 1997, this specimen produced a good quantity of seed that Dr Beever proceeded to germinate.
Although Martha is still positively a female, she also has adequate virile pollen to self-fertilise her flowers. In other words, she is gynomonoecious.
The availability of seed-grown plants is important, especially in the planting that DoC is currently undertaking, as it raises the possibility that, when these trees mature, we may find a fully functional male.
Professor Geoff Baylis was the University of Otago’s first Professor of Botany and was Head of the Botany Department for 34 years from 1945 until his retirement in 1978. He passed away on New Year’s Eve 2003.
Read more about Professor Geoff Baylis on the Royal Society’s website.