The genus Pittosporum is, in my opinion, one of New Zealand's most poorly represented genera in horticulture. Its members include some of the finest shrubs and small trees of the New Zealand flora, but the only species that have traditionally been offered by garden centres or nurseries are (in my opinion) amongst the most inferior of the genus (synonymous with the gardens of 70s and 80s NZ). This regrettable situation has not been addressed, and Pittosporum is still perceived by many as a genus of scrappy, variegated, small-leaved small trees (a situation that must be amended). Pittosporum predominantly occupies tropical and sub-tropical regions of the Southern Hemisphere, as reflected in its mainly northern distribution within New Zealand.

Pittosporum cornifolium
Tawhirikaro, perching kohuhu

Pittosporum cornifolium is an elegant epiphytic species (that is, a species that doesn't grow on the ground; usually on tree branches or rocks) that (despite its usual home) will thrive in a well-drained soil. It often grows on puriri ( Vitex lucens) or rata (Metrosideros robusta) trees, amongst entire communities of epiphytes. These epiphytic communities are remarkable gardens suspended on the branches of our large forest trees, and their constituents can be surprising in their size and diversity.

P.cornifolium is commonly offered in two forms by local nurseries. The mainland form has smaller leaves, which are of a light green, and is variable in its flower colour. It eventually forms a tidy, dense shrub up to 2.5m high (although more commonly 2m). The other form (the Poor Knights Islands form) has darker, larger leaves that are lusher in appearance, and resembles a vireya rhododendron whilst young. It eventually forms a shrub of a similar size and habit as the mainland form. It is a common phenomenon that the leaves and flowers of plants from many offshore islands are larger than those of their relatives of the mainland (a fascinating occurrence that requires further investigation). Both forms are excellent garden subjects for well-drained soil (although my experience has shown that they can withstand surprising levels of moisture in the soil, once established).

It may be that many of the P.cornifolium plants that are commercially available are from a variety selected by Graeme Platt from the West Coast of Auckland (Maunganui Bluff), which was terrestrial, growing in full sun, and exhibited a thicker, more compact form than the species type. However, as it is a naturally variable species, superior forms of the plant may have come into cultivation coincidentally. P.cornifolium ranges from North Cape to the Marlborough Sounds.

Pittosporum dallii

This beautiful species has a very restricted distribution in nature; occurring only in North-west Nelson, an area which is somewhat of a biodiversity hotspot within New Zealand. It is readily distinguishable from all other Pittosporum, on the basis of its dark stems, intensely green, serrated foliage, and the large sprays of cream flowers that are produced in midsummer, during good years. The form of the flowerheads bears a resemblance to the inflorescences of another of our most beautiful flowering plants, Pimelea longifolia (native daphne or taranga).

It has been pointed out by several authors that this species flowers sporadically in cultivation. It is, however, worth cultivating for its foliage and growth form alone. In his seminal work, 'The Cultivation of New Zealand Plants' (1923), Leonard Cockayne wrote of P. dallii as "foremost amongst desirable species for town planting". At the time it was not in cultivation in New Zealand, and it is still little-known within New Zealand gardens - where it is mainly found in the collections of enthusiasts.

Pittosporum dallii is a threatened species (classified as Nationally Vulnerable), which primarily suffers from the depredations of introduced pest animals (deer and possums). It is often found on steep ground (a position in which I have observed this species in the wild, at Cobb Valley). That fact is unsurprising, for one often finds threatened species in such habitats, as they are less accessible to browsing mammals. Lawrie Metcalf has noted¹ that it is capable of tolerating considerable drought. This observation has been borne out in my personal experience, of having planted P. dallii in the extremely dry climate of the Mackenzie Basin, where it has thrived.

Pittosporum kirkii

Pittosporum kirkii is, like its relative P.cornifolium, epiphytic (occurring on rocks or trees) and occurs commonly on the trunk and branches of rata and other larger forest trees. However, unlike P.cornifolium, it is often terrestrial as well. It usually occurs in hilly forest from Mangonui (Northland) to Mt Egmont, from 240m to 900m, and is most plentiful at about 650m.

Pittosporum Kirkii

It forms a shrub from 1.2m to 3.6m high (but seldom exceeds 2m), and has an open habit. A notable feature of P. kirkii is the presence of outsize, flat seed-capsules that adorn the plant following flowering; these are highly conspicuous and very unusual in appearance. It is named after its discoverer, Thomas Kirk, who first collected it on Great Barrier Island.

Due to its place in nature (as a perching plant), Pittosporum kirkii should be given a well-drained position in relatively poor soil, if grown in the ground. However, it is particularly well suited as a pot plant, an application in the garden that recreates many of the conditions in which it grows within nature.

Footnotes

In 'New Zealand Trees and Shrubs : a comprehensive guide to cultivation and identification. 2000. Auckland, Reed Books.'