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Dysoxylum spectabile
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This article was published in The Fringe, June 2015

Kohekohe

The only species of Dysoxylum in New Zealand grows in frost-free, rich soils in lowland forests from the Far North to Marlborough. Belonging to the Meliaceae family it is related to the various species of mahogany including the wide spread Dysoxylum mollisimum subsp. molle. About half of the 80 Dysoxylum species are restricted to our Pacific neighbours, with the rest spread around Asia and countries bordering the Indian Ocean. They all have compound leaves (leaflets in 3 or 4 opposite pairs and one on the end). Like kohekohe they mostly have large leaves up to half a metre long, typical of tropical forest trees.        

Kohekohe also has the typical habit of trees in the genus where the flower spikes burst out in clusters from the trunk and old wood along the branches. This habit is called "caulifery" as when they first emerge the combined cluster looks like a developing cauliflower.  The 30cm long flower spikes have dozens of small flowers. In the past it was considered the flowers were perfect with functional male and female parts, but more recently it is said they are gynodioecious, where all the trees have functional female flowers, but only some of them have functional males.   About a year after flowering the fruit have developed into knobbly brown capsules up to 3cm in diameter, and they ripen just as the next year's flowers are developing. This is clever timing as the birds which have gorged on the fruit will continue to pollinate the flowers when they visit the tree to over-indulge in the flowers' nectar. Between the fermenting fruit and the nectar the birds reach the point where they can be considered decidedly drunk. The fruit are revealed when the capsules split open, showing the bright red/orange flesh surrounding the seeds.

An interesting disease that seems to be confined to Dysoxylum appears as greasy, translucent leaf lesions or 'shotholes' in the leaf tissue. Transmission of the disease is probably by rain splash, but it may also be transmitted from the adult tree into the seed embryo.  The disease seems to be an endemic, bacterial pathogen for which the name Pseudomonas dysoxyli has been proposed.  

It is suggested by some that kohekohe has medicinal properties similar to quinine.   Certainly Maori used it for a number of health remedies, taken as infusions or decoctions.      

Now is the time to go looking for kohekohe to see the flowers on the tree and also to collect the fresh seeds from off the ground. While still in the unopened fruit, the seeds are green and they already have the capacity to produce the chlorophyll necessary for growth. Birds tend to consume a lot of fruit then move to a favourite perch to digest their meal. The result is large clusters of seed deposited in a pile of guano. As soon as the seeds hit the ground they begin to develop their roots. I have found they are often hidden in the leaf litter as nature has a way of immediately covering the guano piles in a mantle of wind-blown leaves. This has the benefit of preventing the vulnerable seeds from drying out before they germinate. 

Go for a tramp in a coastal forest and see what you can find. If you don't go now the rats and possums will beat you to both the flowers and the seed. The quantities consumed by these pests are having a huge impact on the regeneration of our sub-tropical forests.                        

 

 

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