Horticulture Heading

Pennantia baylisiana
New Zealand's rarest tree —
its discovery and propagation

Reproduced from an article by Professor G. T. S. Baylis

From The New Zealand Garden Journal (Journal of the Royal New Zealand Institute of Horticulture), Vol. 2, No. 1, March 1997, pp. 12-13.

The only remaining tree in the wildT. F. Cheeseman was an early Director of the Auckland Museum. He was also the first botanical explorer of the Three Kings Islands. On his visits in 1887 and 1889 he had only a few hours ashore, yet he found six new plants. A more thorough search was clearly warranted but it was not until 1945 that the Museum arranged for a scientific party to camp on the main island. I was the botanist. By this time wild goats had eaten the place out. Part was closely browsed grass but most was kanuka forest or scrub. Cheeseman's novelties survived in small numbers beyond browse range. It was easy to see that the grassland offered nothing new, but the kanuka canopy was broken here and there by other textures and shades of green. I located these places by climbing trees at every vantage point and reached them deviously via bluffs and screes since except in the main valley they were, even for goats, a bit inaccessible.

In these clumps such things as puriri, mahoe and mangeao persisted and I soon found the liane Tecomanthe speciosa and the rangiora with a corky trunk like a cabbage tree - Brachyglottis arborescens. The last little grove that I investigated lay near the highest point of the island down a scree of boulders about 200m above the sea. I was drawn to it by what looked like a karaka. I was soon gazing upon it in disbelief since a third find seemed too much to expect. But 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.

Dr W. R. B. Oliver, our last true biologist equally authoritative about animals or plants was anxious to identify my finds and I sent them to him. Lacking time and experience, I feared I might blunder by getting a family wrong. This danger proved real indeed, for Oliver himself put the pseudo-karaka in the Anacardiaceae, which is close to the karaka family, whereas had I been able to send fruits he would have realized that the resemblance to karaka is misleading, the proper family being Icacinaceae to which Pennantia belongs.

It was a European botanist working with herbarium sheets who realised that the Three Kings specimens were Pennantia: indeed concluded that the tree was just a stray P. endlicheri from Norfolk Island. But herbarium sheets don't tell all - thicker leaves recurving curiously in the sun, stouter stems and flowers on leafless branches rather than at the ends of twigs so distinguish the Three Kings tree, that the two have little resemblance. So when our Flora is next revised either the definition of Pennantia will be broadened to accommodate cauliflory (flowers arising on old wood) or Oliver's genus Plectomirtha will reappear as a member of the Icacinaceae. The former seems the wiser course as P. baylisiana does occasionally flower at a branch tip. Moreover, the objective of taxonomy is to synthesise and there is no synthesis when a species has a genus to itself.

Foliage and flowers

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 "Plectomirtha" beyond doubt.

 

Cultivation of Pennantia baylisiana


It is now 50 years since the tree was discovered and it is still not common in cultivation. This is because the species is dioecious, the sole remaining tree being female. Whilst some self-pollination does occur, nearly all the fruit produced are sterile. In cultivation the species readily cross-pollinates with the kaikomako, Pennantia corymbosa, producing hybrids with intermediate features. One selection from this cross has been named Pennantia 'Otari Debut'.

Propagation is from hardwood cuttings taken in autumn. Rooting can take up to 10 months and young plants will often collapse and die in the first twelve months.

Plants are easy to grow provided they are given protection from frost, and can tolerate shade, growing well under the canopy of larger trees. Trees tend to produce multiple stems and can grow to more than 5 metres high. The main ornamental value of the tree is its large glossy foliage, looking as Professor Baylis said, like large karaka leaves.

Mature trees in cultivation can be seen at the Otari Native Botanic Garden, the Auckland University Grounds, and at HortResearch, Mount Albert, Auckland.

Notes on cultivation by Mike Oates


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Last updated: August 3, 2001