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Ixerba brexioides
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This article was published in The Fringe, June 2016

Tawari

A handsome tree to 10m tall, tawari is endemic to the northern half of the North Island. Curiously, it does not fit well into any closely-related family and has been shunted from Brexiaceae to Escallionaceae. More importantly, in 2008 it was briefly placed into its own monogeneric family named Ixerbaceae, which made it the only NZ species in an endemic plant family. A short-lived honour.

In 2009 it was moved into the previously endemic New Caledonian family of Strasburgiaceae - which was disappointing for botanists of both countries as it is a matter of national pride to have endemic families that do not occur elsewhere. It gives a degree of exclusivity to the vegetation. New Zealand's plant species endemism of 81.9% is behind Hawaii with 89% but ahead of New Caledonia's 79.5%. The order is reversed when the number of species is considered.

New Caledonia at 1.8 million hectares, is slightly larger than Northland, yet has 2,973 species compared to New Zealand's 26.8 million hectares with 2,362 species, and Hawaii's 2.8 million hectares has only 956 species. When you consider a quarter of New Zealand's species are alpine plants above the treeline, it means we are 'species-poor' over the rest of the country when compared to New Caledonia. Of course, compared with many other parts of the world New Zealand is very rich in species.

The "we've been robbed" moment comes when you realise the Ixerbaceae was our only endemic 'family'  meaning the Ixerba was so distinctly different it was not just an endemic genus but had no close relatives at the family level either. Unfair when you consider New Caledonia had five endemic family groups but still retained four, once Ixerba was included in the Strasburgiaceae.

As an endemic species is considered different from any species in other countries, at the genus or generic level the endemic genera are really different, which of course makes an endemic family, really, really different. But in the New Zealand bush it looks only slightly out of place.

Ixerba's glossy leaves have a slightly tropical look, but they are smallish, 10cm x 2cm, serrated and rather leathery with a strange olive-green colour occasionally turning red as the leaf ages. The attractive scented white flowers are clustered in 5 to 10 flowers per panicle on the tips of the branches in late spring. This is one of the few species for which Maori had a special name for the flowers - whakou.

In spring the blossom provides nectar and pollen for bees to make delicious tawari honey. In autumn the leathery seed capsules split to reveal the 5mm glossy black seeds with the orange-scarlet aril attached. It must be full of nutrients because the tui and other frugivores love the fruit and flock around the trees in autumn to gorge on the rather small portion attached to each seed.

Alas, the tawari is a difficult tree to cultivate and so if you live on the higher slopes of the Waitakeres, treasure the tawari which may be growing naturally alongside the kauri in your backyard. 

 

 

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