The New Zealand Plant Conservation Network

Would anyone like to suggest what sort of coprosma hybrid this is? We have exactly two of them, one male (pictured) and one female. Although the photo shows near-horizontal branches, the overall form of the tree is strongly upright and symmetrical, unlike the messier habit of what I presume is one of the parents, coprosma robusta. We have quite a few other coprosmas kicking around, and I wondered whether coprosma crassifolia might be involved. But I await suggestions.

Hi William, The plant you have there is a naturally occurring hybrid between Coprosma robusta and Coprosma propinqua var. propinqua. It is quite common in areas nearing wetlands. It was once referred to as Coprosma cunninghamii by Hook.f. I come across it regularly in the kapiti area, and as far as I know it is sometimes sold in nurseries.

Thanks, Matt. I have heard of that hybrid. If that is what it is, I wonder how it happened on our property, and twice, with the two plants being situated quite far apart. We have no coprosma propinqua on site and I doubt there are any in the vicinity. And we are not close to any wetlands, being on a very well-drained elevated site on the north side of the Manukau Harbour. I guess we blame the birds!

Hi William, Matt is probably correct in identifying this as C. xcunninghamii (a hybrid between C, propinqua and C. robusta), but there are many known hybrid combinations within Coprosma. I have often seen this hybrid a long distance from one or both parents and it is probably because Coprosma females are wind pollinated (so the male plant can be a long way distant) and the fruit is bird dispersed (which could subsequently remove it from the vicinity of the female plant).

Yes that is one of the many variations produced by Coprosma xcunninghamii (C. propinqua x C. robusta) which is found as a introgressive hybrid swarm. This hybrid is very common and widespread, and as Mike notes it can be found well outside the range of either parent - for example on the outer Hauraki Gulf Islands you will find it - despite hybrids being common in Coprosma, very few of the combinations know are numerically common, C. xcunninghamii is one of the few, C.xkirkii another.

Many thanks for the further information. One of the reasons I wanted to ask now is that the female plant, covered with berries, has suddenly collapsed - I think because it has come up in full shade rather than because of the (now annual) drought, and has had to stretch itself very hard to get through to the light. I presume that if I take some of the seeds, they will come up "true to type"?

I've seen large leaved coprosmas suddenly collapse - the leaves rapidly turning black - and have thought it was a root disease/fungus. Drought seems to affect coprosma less than other species such as mahoe. I doubt that the shade would effect the plant as C. robusta likes shade. The fruit "might" come up true - it would depend on who the pollinator was. You would know whether it was true seed when the cultivated plants are young and any hybrids can be weeded out

Funny - on our Manukau Harbour cliff we have lost quite a few copromsa robusta in the droughts of the last few years, but the mahoes have never looked like dying. But I think the idea of a fungus sounds plausible. It has been a very sudden collapse.

Interesting - in the last big drought a couple of years ago I noted mahoe with withering leaves but did it was only later in the drought that C. grandifolia leaves started to wither. A complicating factor is that diseases can have a greater impact on a plants health when it is stressed (like in a drought). I've always mentally attributed plants that suddenly collapse and lose their leaves (often turning black, or totally withering with no recovery following rain or watering) as due to disease or fungal pathogen. Planted individuals seem more susceptible than naturally established plants. Without careful testing it can be VERY difficult to determine the cause of death of plants.