Looking at Coprosma

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In this edition we look at the genus Coprosma, one of the most common group of native plants. They have an interesting history and several features which make them relatively easy to tell apart from other plants.

In New Zealand the genus Coprosma has about 60 different species. Those involved in the Trees for Survival programme will be familiar with two of these species, karamu (Coprosma robusta) and shining karamu (Coprosma lucida) since both plants, because of their tolerance to a wide range of conditions, are widely used in restoration plantings.

Coprosma belongs to the family Rubiaceae, which includes useful plants such as Coffea and Cinchona, yielding coffee and quinine respectively. The genus is also found in the Pacific, Malaysia and Australia but New Zealand is the Coprosma headquarters.

Coprosma robusta

Coprosma lucida

The foetid coprosma - resposible for giving the genus a bad name!

On Cook’s second voyage only two species of Coprosma were found, one of which had a most unpleasant smell, strongly reminiscent of carbon disulphide. As a result the whole genus was given the name Coprosma meaning ‘smell of dung’ which is a little unfair considering only these two species have this noticeably obnoxious smell.  In addition, this plant was given the specific name foetidissima, ‘extremely vile smelling’.  You can find this shrub in coastal to subalpine forest, shrub land and occasionally grasslands – just crush the leaves between your fingers – the foul smell will tell you that it is Coprosma foetidissima!

Coprosmas are all woody and they have opposite pairs of leaves, stipules and pits or domatia can be found in all but the very small-leaved species.

The image below shows opposite leaves (blue arrow), a stipule (yellow arrow) and a domatia (red arrow).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It is thought that stipules which bear tiny tooth-shaped denticles secrete mucilage when young leaves are forming thereby protecting the tender growing leaf tissues.

What domatia or the leaf pits do is not clear. Those who hold that they are shelters for small insects call them domatia, meaning ‘dwellings’. Certainly small insects are often found in the pits, but they could have come upon this convenient shelter by accident. Others suggest that Coprosma pits contain bacteria which fix nitrogen.

If you have a microscope, look inside some Coprosma domatia and see what you can find!

And where are you likely to find a Coprosma?  They are found in a variety of natural environments from the mountains to the coast. They range in habit from creeping mat plants through different forms of shrub to small trees. Their feature of luxuriant verdant green in the larger leaved species, and the quirky textures of the divaricating small leaved species and an abundance of colourful berries make them ideal plants for ornamental gardens too.

Taupata (C. repens) with its shiny leaves and low growing habit occupies coastal habitats.

Coprosma depressa also is a low growing speading plant but it has small leaves and occupies open upland areas.

C. Tenuicaulis is a small leaved erect shrub found in lowland swamps and bogs.

C. colensoi, a small bushy shrub of montane forests with leaves which may be oval or narrow

The fact that Coprosma species grow in such a wide variety of habitats and have adopted many different plant forms in New Zealand demonstrate an interesting phenomenon called adaptive radiation. This is where a plant or animal, once established in a new land, will diversify rapidly into a multitude of new forms which in turn become established in new and different habitats. Maybe there will be an opportunity in a later edition of Tree Talk to discuss adaptive radiation which was an important concept for Charles Darwin in the development of his Theory of Evolution.

Anyone interested in learning more about the genus Coprosma can look up the excellent website called Bushman’s friend and particularly the Coprosma teacher resource.

Accessing a key can help with plant identification and there are keys available on the Landcare Research website – they even have a Mobile App!

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