Plant profiles > Coprosma

Family : Rubiaceae

There are few groups of plants that exhibit such a wide range of adaptations to New Zealand's varied landscapes as the genus, Coprosma. Creeping mats, upright small trees, large leaves, small leaves, berries of many different colours, shade-dwelling or inhabiting open ground; Coprosma really has an astounding variety of habits, characteristics and tolerances.

As might be expected, this makes Coprosma a very useful and versatile genus for gardeners and landscapers. In recent years, this genus has become doubly useful through the evolution of garden tastes - to embrace a wider range of native plants (especially those with small leaves, and interlaced branching structures). Thankfully, this development means that there is now a greater focus on the merits of our many species of Coprosma (rather than man-made cultivars).

Despite the wonderful range of species on offer, the genus does suffer from a bit of a PR problem. For years, the main varieties to have been cultivated have been variegated abominations (of multifarious hues) and characterless hybrids (including many varieties of soul-numbing, creeping 'roundabout' shrubs). Coprosma spp. are prone to such human tinkerings, for certain species hybridise readily, even within nature (a fact that was commented on by both Leonard Cockayne and W.R.B. Oliver¹).

Due to this unholy alliance of varieties (some garish, others featureless) the name 'coprosma' has become, to many people, a byword for the kind of native that you reluctantly plant because nothing else will work (similar to the oft-maligned Pittosporum).

However, as noted above, the tide has turned with increased interest in New Zealand's small-leaved shrubs (known either as filiramulate or divaricate shrubs²). Most of our Coprosma spp. fit into this category. Several of these species (such as Coprosma virescens, C. rugosa and C. propinqua) form billowing clouds of foliage, in a range of colours (these colours are sometimes conferred by the stems rather than the leaves). Some (including C. cheesemanii and C. petriei) form creeping mats that adorn banks and open ground in our montane areas, whilst other species (like C. distantia, C. neglecta and C. spathulata ssp. hikuruana) tumble over our northern coastal cliffs.

A major part of the appeal of so many small-leaved species is that the reduced leaf size draws attention to the 'architecture' of these trees and shrubs. Now, the use of the word 'architecture' is not some lame attempt to make plants seem more hip; it is an actual term that is used by botanists to refer to a plant's branching structure. Branches may be straight or arching; they may be densely packed or spaced wide apart; they may protrude in dense, voluminous masses or splay out in rigid fans; or they may be distinctly tiered.

I always associate these beasts with Auckland painter, Michael Shepherd, who has a special affinity for them, and all their 'twiggy' mates (Michael is pictured, left, admiring Coprosma rugosa in the wild, at Ben Ohau). Michael's appreciation of these as garden plants is more comprehensively covered in an essay (from the 'Essays' section of our website) that we co-wrote, entitled 'Scrub aesthetics'. Coprosma rhamnoides is foremost among these species in Michael's affections, although he grows a diverse range of species in his Auckland garden. C. rhamnoides is a relatively compact shrub that occurs in a variety of forms, but is notable for its tiered branching habit, often weeping stems (at the tips), and the profusion of berries (which range in colour from red to almost black) that it produces.

This last characteristic is a particularly appealing incentive for cultivating our species of Coprosma; for the quantity of fruits that they produce can provide a valuable food source for native birds and lizards. These fruits come in an amazing array of colours, including white, orange, yellow, red, iridescent blues, shades approaching black, and translucent, milky hues. Aside from their wildlife value, they also add immensely to the aesthetic appeal of Coprosma spp., contributing small flashes of colour to a planting.

New Zealand has c. 53 species of Coprosma, which is almost half the worldwide number of species within the genus³. These occur throughout the New Zealand botanical region, from the sub-tropical Kermadec Islands to the Subantarctic Islands in the south. Its unfortunate (and misleading) name is derived from the Greek word for manure (kopros), and arose from the unpleasant odour of one of the first species to be collected (C. foetidissima).

Coprosma petriei

Moss-like plants constitute a plant type that is on many people's wishlist - frequently inspired by serene visions of Japanese gardens. However, this is a difficult effect to achieve in gardens, as the kinds of conditions that promote verdant moss growth (like those seen in Japanese temple and palace grounds) are not replicated in most gardens.

In New Zealand, a moss-like effect is most frequently attempted through the use of one of our species of Scleranthus. However, this plant is regularly specified in situations in which its lifespan is limited - due to factors such as high rainfall or humidity, or a lack of air movement. Scleranthus is by no means the only genus that is suited to this role, and one of the other leading candidates is the diminutive Coprosma petriei.

This is an extremely rugged species that survives in some of the most unlikely places, such as the rabbit-ravaged short grasslands of the Mackenzie Basin, or on exposed, rocky ground in montane areas. Although the plants in the photo above exhibit a brownish-green colour (due to the tough conditions on the side of Mt John at Tekapo), certain forms of Coprosma petriei have dazzling emerald-green foliage within garden conditions.

C. petriei is one of those surprising mountain dwellers that will grow in many different parts of the country, even in the warmer north. We are growing it very successfully at a garden in the inner suburbs of Auckland, where it wends its way around the base of other native shrubs. Terry Hatch has also grown extensive carpets of it in his own Pukekohe garden for a long period, in both open and slightly shaded conditions.

Some experience in growing this species has shown that it tends to get a better start where it can be afforded a small amount of shelter at the beginning (from an adjacent small shrub or rock), and then creep outwards towards the open conditions that it prefers.

This seems to decrease drought stress on young plants which, although they are extraordinarily resilient to arid conditions in nature, can suffer from drying out in their first season. As with so many plants, establishment is the critical phase.

Coprosma petriei commemorates Donald Petrie, one of New Zealand's early botanical figures. Petrie was a highly respected botanist, who searched for plants in many parts of the South Island (in particular), and was renowned for having a careful eye (regarding the observation of plants).

Coprosma propinqua
Mingimingi

This obliging species can lay claim to the dubious honour of being one of the most promiscuous plants within the New Zealand flora. Coprosma propinqua, it seems, will sleep with just about any tall, dark stranger whose pollen happens to blow into town⁴.

It certainly has a great number of opportunities to come into contact with other species, for C. propinqua grows in a huge range of habitats throughout New Zealand (from dry mountain slopes to lowland swamps). In line with this adaptability, it takes on a diverse range of forms, from low-growing hummocks on the coastline to 3m tall, rounded shrubs (or even higher).

Within older literature, authors often make the comment that New Zealand's small-leaved shrubs (or 'filiramulates'²) are sufficiently similar that they can be hard to discern. This is, of course, rubbish in a great number of cases. Several species with coloured stems (like Muehlenbeckia astonii and Coprosma rugosa) are very easy to distinguish, whilst the growth forms of others (like Coprosma rhamnoides and C. acerosa) make them unmistakable.

However, in the case of Coprosma propinqua, there is a fair amount of truth to this statement, for some other species (notably C. rigida and C. crassifolia) approach it very closely in appearance. This is reflected in its specific epithet, which can be translated as 'closely resembling' - in reference to its similarity to other species.

Falling into this trap, I had always confused plants that I was viewing in the Mackenzie Basin, and grey scrub from nearby areas, with Coprosma rigida (especially because northern forms of C. propinqua look so different from their stiffer southern namesakes) - until I was corrected by the Nelson botanist, Shannel Courtney.

We have planted this dryland form of Coprosma propinqua in our Tekapo garden, propagated off local stock (from a scrub remnant just 60m from the house). A major reason for specifying it is that it is one of the last native plants to endure in degraded ecologies, and is therefore an excellent garden plant for that demanding climate. Another reason is that its contained form makes it a fine structural shrub for gardens, as it will reach around 2m and require almost zero pruning.

The form that is pictured to the right, growing at Titahi Bay, is an example of the low-growing forms that hug rocks on the coastline. Examples of this form that I have seen bear brighter green leaves than montane types (which assume a browner hue, due to the smaller leaf size and duller leaf colour). These coastal forms are useful garden plants, that make an attractive counterpoint to their bolder-leaved neighbours. In their case, it should be remembered that, in garden conditions, they will not remain as prostrate as they do under the constant battering of coastal winds.

There is a particularly leafy Chatham Island variant, C. propinqua var. martinii, that grows in two forms; one that develops into small trees, the other growing as a creeping shrub. The latter is sold on mainland New Zealand as Coprosma 'Taiko'. In northern parts of New Zealand, C. propinqua is frequently associated with swampy sites, and has comparatively flexuous branches and long, narrow leaves (combining to give it a looser appearance).

Coprosma virescens

In recent years, Coprosma virescens has become increasingly popular within gardens, due largely to the attractive orange colour of its stems. These are softened by the pale green foliage, to give it a more delicate colouration than its lower-growing relative, C. rugosa (which exhibits quite vivid orange hues). C. virescens tends to grow as a relatively upright tree, with 'clouds' of foliage tumbling over each other. The smooth bark, which is patterned in grey and green, is an additional attraction that rewards closer observation. Like other small-leaved trees and shrubs, it is a very good plant for providing a sense of depth within gardens.

It is primarily a plant of cold localities on the drier eastern sides of both main islands (occurring from the centre of the North Island south), where it grows in shrubland and on forest edges. The photographs below are from land adjacent to a forest remnant in Banks Peninsula, an area in which Coprosma virescens is particularly common.

Despite the fact that it is native to cold, dry parts of the country, Coprosma virescens can be cultivated throughout much of New Zealand (including as far north as Auckland). However, it is less suited to planting in warmer, humid regions than some other small-leaved trees of similar dimensions (such as Pittosporum obcordatum, Melicytus micranthus and northern forms of Myrsine divaricata).

Coprosma virescens is one of the few native trees to be either wholly or partially deciduous, although it remains evergreen in warmer locales. The specific epithet, 'virescens', means 'becoming green'⁵ - possibly in reference to the greenish bark⁶.

 

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Footnotes

1. In his monograph on the genus, W.R.B. Oliver noted the relatively common occurrence of hybrids between some species, going on to state that in some populations, hybrids are as numerous or more plentiful than plants that are true to type (for the respective species). Cockayne's observations on Coprosma hybrids were presented in his 1923 work, 'Hybridism in the New Zealand Flora' (a contribution towards the British journal, 'The New Phytologist').
2. The term 'filiramulate' is an adjective that was adopted by botanists, as a superior alternative to the word 'divaricate'. It is considered to be a better term for this type of shrub, as 'filiramulate' refers to the internode length in relation to leaf size, rather than the literal meaning of 'divaricate', which is to branch widely (at roughly a 90 degree angle). Not all shrubs that fit within this group of plants branch at wide angles, therefore 'divaricate' does not describe this group of plants well enough.
3. This is the figure provided by Landcare Research, who must be considered the authoritative resource on this matter. This figure may change on occasion, as new entities are recognised (or some reduced back into other species), and some botanists may have differing opinions on the validity of certain species.
4. It is listed as hybridising with 14 other species, according to Landcare Research's 'Coprosma Key' - see www.landcareresearch.co.nz.
5. As stated within 'Meanings and origins of botanical names of New Zealand plants' (Taylor, M. 2002. Auckland Botanical Society Bulletin 26.).
6. In his description, Petrie did not specifically explain the reason for this title; although he made special reference to the smooth, greenish bark.

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