This interesting genus of shrubs and small trees occupies a wide variety of habitats within New Zealand. The species that constitute Melicytus are extremely variable in appearance, ranging from the small-leaved, stiff hummocks of Melicytus alpinus, a shrub species which inhabits drier areas in southern parts of New Zealand, to the much larger-leaved M. ramiflorus, a small tree which is a very common component of forest throughout the country.

Many Melicytus species are adapted to difficult conditions within nature, making them worthy candidates for landscape use. One of the most spectacular examples of this is the ability of M. crassifolius to grow in the face of biting gales either side of Cook Strait. Although mahoe (M. ramiflorus) is commonly used within revegetation programmes, and M. crassifolius is increasing in popularity as a landscape plant, the genus is under-utilised within horticulture.

The exact number and delimitation of the species of Melicytus has been subject to a certain amount of confusion, and is being further investigated by botanists. The genus was previously thought to contain just 12 species (almost exclusively confined to New Zealand), but it is now thought that there may be in excess of 20 species (including some in Australia and Norfolk Island).

In botany, it is sometimes difficult to determine where legitimate species begin and end, as many plants readily hybridise between species (hybridisation is, in fact, considered to be a major factor in the formation of new species). This is particularly true of Melicytus. Another complicating factor is that isolation causes slight differences within local forms of species, leading to the question; 'At what stage is a local form defined as a distinct variation within a species, or as a separate species ?'. This is especially relevant to the complex of species which are related to Melicytus alpinus.

Melicytus alpinus
Porcupine bush

Amidst dry pasture, stonefields and scrub of the South Island (and southern North Island), intriguing hummocks of porcupine bush dot the landscape. The common name tells us something of the appearance of these shrubs, although they could equally be described as 'living stones'. When viewed growing en masse within pasture, they seem like groups of unusual soft boulders, or (to the fertile imagination) the kind of strange 'animist' spirits that mightn't be out of place in a Hayao Miyazaki film.

This resilient species is one of the last bastions of native vegetation in heavily modified landscapes of the South Island high country, probably on account of its stiff, unpalatable stems, interlacing growth habit and drought resistance. The new growth on M. alpinus consists of short leafless sections of stem, giving the plant its spiny, porcupine-like appearance, and ensuring that the bulk of the leaves are held within the canopy (an adaptation that will help decrease heat and drought stress in extreme climates).

The striking appearance, compact growth and resilience of this species make it an excellent garden and landscape plant for drier southern parts of New Zealand. It looks especially good when planted in association with rocks (as it often occurs in nature), in which the contrast of rock and plant highlights the dynamic branching structure of the porcupine bush. M. alpinus is relatively slow-growing, and is best suited to the role of a low, sprawling shrub within gardens. However, over very long periods of time, it can develop into dense shrubs to 1m high and 2m wide.

As with many native species, close inspection rewards the viewer with exquisite details, such as the copiously produced hanging flowers that are borne on plants in late spring and early summer. These are followed in late summer by conspicuous white or bluish berries, which provide a valuable food source for native fauna, such as lizards.

Melicytus obovatus

There are several notable examples of native shrubs that, despite having been hitherto ignored for such purposes, are well suited as hedging. Indeed, many of these are superior to the exotic species that are the default amongst many landscapers and gardeners. This species is perhaps the most exciting of these. It may be utilised in the manner of box (Buxus spp.); but possesses a brighter, more attractive hue of green, is more drought-tolerant, and (as Pukekohe nurseryman, Terry Hatch, points out) it doesn't smell of cat pee (one of Buxus's least endearing characteristics).

It is baffling that M. obovatus has thus far received almost zero attention from horticulturists, as its bright colour is an excellent asset within gardens. This is possibly related to the way in which we often evaluate garden plants; that is, by looking for extraordinary characteristics, rather than assessing the overall form and character of a plant (and its relation to the nature of our landscapes).

I was switched on to the potential of this species by a little piece of visionary planting in a confined raised bed, outside the former site of the National Bank on Dominion Rd. The shrubs (which are shown in the photograph above) thrived in this difficult, windswept location, and their bright green colour and compact form stood out. They were an example of the kind of aberrant pieces of planting that can teach us much about using native plants, if we observe them. Sadly, they have since been removed, as part of replanting work.

Botanically, Melicytus obovatus is a slightly confusing entity, as it comprises several distinct forms, that have been recognised as separate within Eagle's Trees and Shrubs of New Zealand (2006)¹. These will presumably be treated in a more authoritative manner in the future, when the genus receives an overdue revision. According to the aggregation of forms described within Eagle's, the true type of the species, M. obovatus, is native to limestone areas of Nelson, whilst an allied form entitled M. aff. obovatus (i) is the plant that occurs on the mainland coastline and islands of Cook Strait. The latter is the form that we most commonly plant within gardens.

There are also unusual variants from isolated limestone areas of Northwest Nelson (notably Mt Burnett), and an intriguing form (possibly of hybrid origin) that occurs only in the vicinity of Titahi Bay. The Titahi Bay plant shows outstanding potential as a low-growing shrub, with an even more compact growth habit than its close relatives, and glossy, comparatively dark leaves. In contrast, the Mt Burnett form assumes an attractive, arching branching pattern, and has narrower leaves than other plants of the M. obovatus complex. This arching habit forms an excellent frame through which compact climbers (such as the form of native Clematis commonly known as C. hookeriana) may wind their stems.

The Cook Strait form - M. aff. obovatus (i) - that we plant most frequently attains a height in excess of 1.5m tall, if left untrimmed. However, as it takes so well to regular pruning, it can be maintained as low as one foot high. We normally specify this plant to be pruned in a pseudo-formal fashion, which evokes the naturally compact shape that exposed coastal conditions impose upon such shrubs in nature. It is important to note that one should prune the tips of leading branches early in the life of the shrub, to encourage the development of a dense habit later as the plant matures. This is, of course, a rule that should be applied to many other shrubs in the garden.

Unsurprisingly for a plant that inhabits cliffs and rocky ground, Melicytus obovatus should not be planted in overly damp ground, and care should also be taken that soil or mulch is not built up over the base of the plant (although the latter is true for most shrubs). It is tolerant of a range of light conditions, assuming a more sprawling growth habit within shade. Assuming that it is provided with reasonably well-drained conditions, this species is largely untroubled by pests and diseases; yet another characteristic that places it as a superior native alternative to the usual suspects trundled out for structural planting within the garden.

Footnotes

Eagle, A. (2006) Eagle's Trees and Shrubs of New Zealand. Te Papa Press, Wellington.