This genus of beautiful trees exhibits an unusual characteristic, which provides it with its name. The members of the genus, Phyllocladus, are almost completely devoid of true leaves, and have instead phylloclades (also known as cladodes), which are flattened stems that perform the role of photosynthesis. There are six species of Phyllocladus; three of which are endemic to New Zealand, one from Tasmania, one from Borneo and one species which occurs in New Guinea and the Philippine Islands.
The mountain toatoa is a significant feature of subalpine scrub throughout much of the country. It is a very attractive species, that is easily discernibly within these high-altitude plant communities – due to its highly ordered growth habit and usually bluish-grey foliage.
It should be pointed out that the botany on P. alpinus is currently unresolved, and it is thought that it actually comprises three distinct entities. Most forms that are seen within cultivation conform to the form that will probably continue to be called Phyllocladus alpinus. For the purposes of discussion, the other forms will be termed herein as P. alpinus (ii) and P. alpinus (iii)1.
The most important forms from a horticultural point of view are P. alpinus and P. alpinus (iii). Put simply, the former is usually a smaller plant, occurs at higher altitudes, and is found from the central North Island south. The latter (pictured below) is more asociated with lower altitude, forested habitats, grows to a greater height (up to 12m tall), has yellowish-green ‘foliage’2, and occurs from the Coromandel (on high points) southwards. From here on, the focus of this profile will be on P. alpinus, as that is the plant that most gardeners will encounter.
P. alpinus forms a shrub or small tree, that can reach 6m tall – but is often 3m or less within the exposed mountain sites that it occupies. The ‘foliage’2 varies in colour, but is commonly a very attractive glaucous (bluish-grey) hue. It is extremely slow-growing (especially within the harsh habitats that it is able to withstand), although its growth is much speedier under sheltered conditions.
We have used mountain toatoa throughout the Tekapo garden (that is featured in the portfolio), as part of the shrubby structure of the garden. Whilst researching for that planting, I was interested to find out that Phyllocladus alpinus would have once been an important part of the ancestral vegetation in this cold, dry part of the country – especially on infertile sites.
This is doubly interesting, as this species is not currently seen throughout most of the lower reaches of the Mackenzie Basin. In some cases, over-zealous ecologists or botanists maintain that plants that do not presently occur in an area should not be planted, in the name of eco-sourcing. However, as studies of vegetation history can show us, we should not necessarily just look towards the scraps of what remains when deciding what to plant (as long as our judgements are informed).
When I plant gardens, there are certain plants that I hope will last for a very long time and contribute to the wider landscape, and those whose role is more ephemeral. Of the former category, the most important plant is the toatoa; a tree that should be seen more frequently in New Zealand gardens, particularly in northern New Zealand (as it is endemic to the top half of the North Island).
Sir Joseph Hooker (who wrote the first comprehensive flora of New Zealand) proclaimed it “the most charming of all the New Zealand pines.” It is interesting to consider that the toatoa is a conifer, as its appearance is quite atypical for a conifer – bearing, as it does, pinnate, broad “leaves”. The similarity of the cladodes to leaves of members of the carrot family gave rise to the common name of its near relative, the tanekaha (Phyllocladus trichomanoides), which is generally known as the “celery pine”. The toatoa forms a symmetrical, tapering tree, up to 15m tall (but only reaching 4.5 – 6m in gardens), with a trunk up to 60cm diameter.
It is easily distinguishable from its near relative, tanekaha (which grows in the same districts), by the size and colour of its cladodes (they are larger and often have a glaucous or bronze hue to them), and its more upright branching habit. On a botanical note, the toatoa is also distinguished from its New Zealand relatives by the fact that it can be dioecious (meaning that male and female flowers are borne on separate plants) or monoecious (separate male and female flowers on the same plant). The other New Zealand species (P. trichomanoides and P. alpinus) are always monoecious.
Several authors of books on native trees and shrubs for cultivation have expressed consternation at why it has seldom been grown in New Zealand gardens. This would appear to be due to difficulties with propagation (cuttings are difficult and seed is not easy to procure at the right stage), and also due to a lack of commercial interest – for problems with propagation can often be resolved readily with investigation by nurserymen. A few specialist nurseries put the effort into propagating small numbers of toatoa for sale.
Phyllocladus toatoa was previously called Phyllocladus glaucus (“glaucus” on account of the bluish-green hue of the young foliage), but the name was changed in 1996. This was because the initial description for the species was based on the examination of a cultivated specimen of the Tasmanian species, Phyllocladus aspleniifolius, in France in 1865 (not a toatoa at all).