Single sex trees or Dioecious in New Zealand
15 September 2020

New Zealand is full of many unique plants & animals. One aspect of our native plant life that attracts attention is the fact that many plants are of a single-sex or dioecious (two houses). 13% of New Zealand plants versus less than 5% in the United Kingdom are dioecious and many other New Zealand plant species exhibit both single-sex plants & plants with both sexes on the same plant (just to keep botanists on their toes).

If you have been for a walk through the forest lately looking carefully you may have noticed that many members of the Coprosma family where flowering. You may have also noted that different plants have quite different looking flowers.










Coprosma – all dioecious, have small unshowy wind-pollinated flowers, very unlike the rest of its greater Rubiacaea family such as coffee that has vibrant flowers.

Dioecious plants do have a much higher rate of genetic variation in their seeds which gives a greater range of variability within a species and therefore increasing chances of surviving in a wider range of habitats & changing environments.

Coprosma rhamnoides female flowerKanono Coprosma grandifolia male flower

A major downside is that with forests destroyed and limited adult plants remaining there is the risk of pollen bearing male plants not being close enough for the wind to carry the pollen to fertilise female seeds. In Eskdale reserve, there are only a few adult Rimu trees left and most are male leaving only one or two female trees left to produce seeds. As the trees respond to climate cues to flower a dispersed population may not flower at the same time– running the risk that the rimu will eventually die out in the reserve.


Derek Craig

Restoration Nurseries Manager

Kaipātiki Project 



Learn more about Coprosma

Coprosma Spathulata

Coprosma Rhamnoides
Coprosma Macrocarpa