Astelia

Astelia is a Southern Hemisphere genus, comprising around 29 members. They are commonly termed the “perching lilies”, but this name is slightly misleading as many of them are not predominantly epiphytic in habit. Those species that are epiphytic often form a conspicuous component of the upper layer of our forests; those “communities in the sky” that bedeck the branches of our forest trees. The name is derived from Greek (meaning ‘lacking a stem’) and refers to the tufted, basal growth form of the plants.

In recent times, they have deservedly become popular in New Zealand gardens, due to their strength of form, tough constitution, and a trend towards ensiform (sword-shaped) leaves. Most attention has focussed on the Chatham Island species, Astelia chathamica, but there are several superior species from closer to home (like the locally-occurring A. banksii and A. grandis) that we should be planting in our gardens.

They produce flowers in panicles (an inflorescence form similar to that of the cabbage tree), and produce large quantities of berries in autumn. Māori used to eat these berries and used the flowers too, producing a face paint from them. They are known collectively in te reo Māori as “kakaha”.

The genus Astelia consists of around 29 species, and it is centred within the Pacific (with outliers as far afield as the Falkland Islands and Mauritius). Its numbers were recently expanded by a botanical change, whereby the few species from the erstwhile genus Collospermum were shifted into Astelia. New Zealand has fifteen species, all of which are confined to our shores.

The wharawhara is a common sight around the coastline of Auckland, adorning cliffs and trees with its strappy, silvery leaves. If given a well-drained soil, it is easy to cultivate, and has become a popular plant in Auckland’s gardens. It grows slowly and can reach 2m tall, but an eventual height of 1.2-1.5m high is more common in cultivation.

Although it grows more slowly than A. chathamica, it is (in my opinion) a superior species for the garden; as it does not reach the massive dimensions of A. chathamica and maintains a tidier form (in addition to the fact that it is a locally-occurring species). It often grows in association with pohutukawa, as this is the dominant species in much of the local coastal vegetation.

It was said to be the home of the fairies (by ancient Māori), a mythological belief that is not entirely fanciful, as the astelias (particularly the epiphytic species) are epicentres for forest life. They are used by forest birds as bird nests, support invertebrate animal populations, support other plant life, and provide food for the birds. Māori also used the young, silvery leaves as adornments. It bears the specific name of New Zealand’s most famous botanical pioneer, Joseph Banks, who was naturalist (with Daniel Solander) to Captain Cook’s first voyage to New Zealand.

In keeping with the tough nature of its habitat, the swamp astelia is a brute of a plant – albeit a particularly handsome brute. Viewing it at what is perhaps the strongest remaining population within the Auckland region (where it has become uncommon in the wild), the savage character of its habitat impressed itself very tangibly upon my person – as my colleagues and I pushed our way through thick swathes of the aptly-named cutty grass (Gahnia xanthocarpa).

As unappealing as a stroll through a swamp of cutty grass may seem, it is worth the effort to see a plant as majestic as Astelia grandis in a natural plant association. This is a plant that should be used extensively within Auckland gardens, as it was initially described as a distinct species from plants occurring near Ponsonby Road (that were collected in the 1860s). It has already become a flagship species for restoration work in Hamilton, where it is an impressive and characteristic component of the original flora of that city’s gullies.

Astelia grandis is notably absent from most native horticultural literature, although Lawrie Metcalf described it as a “fine and bold garden plant”¹. This is, in my opinion, partially due to writers assuming that its potential role in gardens is satisfied by the robust, silver-leaved A. chathamica. Foliage colour can often cloud our judgements on the gardenworthiness of plants, blinding us to more important characteristics, such as how a plant holds its form over time.

This scenario is a classic case in point. Astelia chathamica has good point-of-sale appeal (with its wide, silver leaves) but tends to lose its form quickly within northern New Zealand. This makes sense when one considers the equable, maritime climate of the Chatham Islands – as opposed to Auckland’s climate (where growth is checked less by environmental conditions). Astelia grandis can play a similar role in gardens, but keeps its shape much better over the years – as it is adapted to the seasonal patterns of northern New Zealand.

The common name of ‘swamp astelia’ is a little misleading with respect to the range of conditions in which A. grandis will perform. It is a versatile plant that can tolerate seasonally dry conditions – although where considerable drought is experienced, rupestral species like Astelia banksii or A. solandri should be planted instead. As a species that occurs within both open habitats and swamp forest, A. grandis is amenable to planting in the sun and semi-shade.

Swamp astelia is found throughout the North Island, and grows down at least as far as South Westland² – where it is a significant component of the kahikatea forests that represent some of the best extant examples of our lowland swamp forests.

Although common names should not be paid as much heed as their scientific counterparts, they are sometimes especially evocative. My favourite example is the widow maker (Astelia hastata) – a name that takes us inside the world of the men that worked our forests in earlier times, and carries information about both the physical character of these plants and their position within the forest.

Before anybody gets spooked into continually looking upwards during bush walks, lest they get squashed by a nest of kahakaha, I should qualify the above description. The main reason that tree fellers were justifiably wary of these plants is that they were shaking and eventually destroying the trees in which Astelia hastata (which was until recently known as Collospermum hastatum) perches. For this reason, clumps of kahakaha could become dislodged (or break the branches on which they rest), and fall from a great height to kill a man. So unless you’re planning on chopping down a forest giant, or taking a leisurely stroll in the forest during a hurricane, there’s nothing to worry about.

Kahakaha are more specifically adapted to a life off the ground than other species of Astelia the most notable distinction being their rounded leaf bases– that effectively form tanks for the storage of water (similar to the way in which bromeliads store water in their leaf bases). Roots subsequently grow up into these water reservoirs, thereby providing them with an alternative supply of moisture from the usual sources that plants rely upon³.

In her seminal book on gardening with native plants⁴, Muriel Fisher notes the way in which asteliads⁵ “give our bush such a tropical look”. This observation is borne out particularly well in the case of Astelia hastata, which forms majestic nests of its wide, sword-shaped leaves in the canopies of our forest trees.

Although predominantly epiphytic, kahakaha is sometimes found growing on the ground – especially in rocky sites like Auckland’s lavafields, the best extant example being Rangitoto Island (pictured above). Such habitats provide similar conditions to the branches of trees; and as a result, epiphytes like Astelia hastata find opportunities within them.

A. hastata is not commonly thought of as a garden plant, but it makes a striking species for both the forks of trees and extremely well-drained situations – such as at the base of trees and within crib walls. We have seen it used in the latter application, to great effect, at the Hortresearch grounds in Mt Albert, Auckland (in combination with another epiphytic/rupestral species, Xeronema callistemon). If one is to plant kahakaha in the ground, it is best to surround the base with stones that are dug into the ground, and place the plant in a slightly raised position.

The above photos show a kahakaha in flower, during autumn. I noted that the flowers were the subject of much interest by visiting honeybees, who were deriving nectar from the extended flower-spikes. This piqued my curiosity about which animals find sustenance from these large inflorescences and the subsequent fruits.

One fascinating creature for whom Astelia hastata is an important source of food (in the form of nectar, pollen and fruits) is the lesser short-tailed bat – an increasingly rare inhabitant of our forests that is only found within New Zealand. As may be expected, the fruits (which vary in colour from yellow through to red, depending on their stage of development) are also visited by native birds, including tuis and wood pigeons⁶.

Astelia hastata grows from the Three Kings Islands (off the northern tip of the North Island) down to the northern end of the South Island⁷. The specific epithet, ‘hastata‘, means spear-shaped; in reference to the anthers, I assume (not the leaves as I had previously surmised – they are in fact sword-shaped)⁸. It generally grows to between 1 and 1.5m tall, and can form substantial clumps that are several square metres in area over a long period of time.

Astelia trinervia is a common and conspicuous constituent of kauri forest, as implied by its common name. In the kauri forests to which it is etymologically bound, it combines with kauri to form a very beautiful aesthetic association – whereby the impressive, bolt-upright trunks of kauri emerge from a massed understorey of tussocks of A. trinervia. Typically, trees and shrubs in the understorey are either insubstantial or sparse, lending such scenes a cathedral-like atmosphere  – as there is an empty, ethereal space that sits between the tussocks and the vaulted canopies high above.

Kauri grass is a species which is hardly ever found in cultivation, by virtue of the fact that it is slow-growing – something which is actually a good attribute for many garden plants, but is often considered a disadvantage by gardeners. It bears attractive inflorescences of small flowers in autumn and early winter, which develop into red berries in the following seasons.

It is essentially a northern species, being confined to the northern end of the North Island and west Nelson in the South Island. Kauri grass is normally terrestrial, only occasionally occurring as a low epiphyte. It forms dense tussocks up to 2.5m tall in forests, but is usually smaller in cultivation. One interesting cultural fact regarding kauri grass was recounted by Thomas Kirk in his 1872 paper on New Zealand members of Astelia⁹, wherein he noted that its leaves were widely used for thatching at the time.