New species of endemic ngaio recognised for the Chatham Islands

Chatham Island ngaio ([i]Myoporum semotum[/i]) flowers. November - Pitt Island.  Image: Peter J. de LangeChatham Island ngaio (Myoporum semotum) flowers. November - Pitt Island. Image: Peter J. de LangeNgaio (Myoporum laetum) is an important rongoa and taonga for many iwi. As many a tramper will appreciate an infusion made from crushed leaves is an excellent way to soothe and treat grazes and infected wounds, while I can personally vouch that burning sprigs of fresh foliage does indeed, as old time Maori advised, repel even the most determined mosquitoes and sandflies! Also in Maori mythology it is a gnarled old ngaio tree that is said to have accompanied Rona on her involuntary trip to the moon. There can be little doubt that the humble ngaio has a special place in many peoples hearts, not only because of its medicinal properties and role in Maori myths but also because it is a hardy, fast growing, drought tolerant tree that provides excellent shelter in coastal areas from strong winds. Ngaio is also popular with gardeners because it produces a profusion of purple-spotted white flowers almost throughout the year, and these are followed by equally attractive quantities of purple or pink fruits. However, despite all these charms and uses it should be noted that all parts of the plant and especially the foliage are also extremely toxic (Connor 1977).

Until recently Ngaio used to belong to the Myoporaceae a small southern hemisphere family. However, this has recently been merged with the Scrophulariaceae (see APG III and comments therein), itself a formerly large family in the New Zealand native flora but one which due to molecular wizardry is now represented here only by indigenous Myoporum and a whole swag of otherwise wholly naturalised genera. Myoporum is also species poor in New Zealand (the majority of the species occur in Australia - Chinnock 2007). In the Flora of New Zealand series Allan (1961) recognised only two species of Myoporum native to the islands, ngaio (Myoporum laetum), and M. debile. Myoporum debile has since been transferred to the wholly Australian genus Eremophila as E. debilis. It is no longer regarded as indigenous to New Zealand, with the few wild occurrences of this otherwise eastern Australian endemic now believed to have stemmed from either past deliberate plantings or failed naturalisations form these. Either way, whatever the explanation for these past occurrences, Eremophila debilisis not only extinct in the wild in New Zealand but also no longer considered part of our indigenous flora (Chinnock 2007).

Shell akeake / Chatham Island ngaio forest on Pitt Island.  Image: Amanda BairdShell akeake / Chatham Island ngaio forest on Pitt Island. Image: Amanda BairdIn the 1980s Bill Sykes added a second indigenous species of Myoporum to New Zealand, M. kermadecense, as an endemic of the Kermadec Islands (Sykes 1987). It is a very common tree in the coastal forest of Raoul Island, and one of the few woody trees on Macauley Island. Chinnock (2007) has since relegated that species to the rank of subspecies within M. rapense, as subsp. kermadecense.

In December 2007 on a visit to the Chatham Islands Peter Heenan happened to observe some Myoporum seedlings being grown for the Mangere Island restoration project by Bridget Gibb of the Department of Conservation, Chatham Islands Area Office at Te One. Puzzled by the lighter green foliage and scarcely evident secretory cavities of the leaves, Peter begged a few plants for further study in New Zealand. From these plants he became convinced that the Chatham Islands had a new species of ngaio. Later in May 2008 Peter and I returned to the Chatham Islands and in the course of other duties undertook a careful investigation of ngaio on the islands. We soon realised that there were indeed two distinct races, one matching New Zealand ngaio (Myoporum laetum) which we only saw on Chatham Island, and there only in sites where it was being cultivated as wind breaks, or in places where there had formerly been houses; the other we only saw on Pitt and the adjacent outlying islands. That race matched the plants being cultivated by Bridget Gibb for the Mangere Island restoration project. On an especially cold night at Caravan Bush, being unable to sleep, Peter and I did what any sensible botanist would do have a healthy argument about the pros and cons of recognising a new species of ngaio! After all we both knew that ngaio is notoriously variable in New Zealand and that other attempts to segregate parts of that variation with formal names had met with considerable resistance. So we felt it absolutely essential that we considered all scenarios before proposing another new species. Therefore, between 2008 and 2010 we undertook a careful evaluation of the variation exhibited by ngaio (and also the Kermadec ngaio) throughout New Zealand. In particular Peter Heenan undertook a painstaking analysis of the size and numbers of secretory cavities of leaves sent to him by myself and other botanists we'd contacted for this task, from ngaio populations throughout New Zealand. Along the way we examined growth habit, bark texture, flower sizes and colouration, we also analysed DNA sequence data (Heenan et al. 2010) and looked at chromosomes. Finally we concluded that the Chathams did indeed have two species, one matched the New Zealand ngaio and was probably not native to the islands, and the other represented a distinct element endemic to the islands. This endemic was sufficiently distinct to merit recognition as a new species.

Chatham Island ngaio trunk and branches showing bark.  Image: Amanda BairdChatham Island ngaio trunk and branches showing bark. Image: Amanda BairdOur conclusions have just been published in the New Zealand Journal of Botany (Heenan & de Lange 2011) where the new Chatham Islands ngaio is described as Myoporum semotum. The new species is distinguished from Myoporum laetum by its smoother bark, usually wider leaves; by the leaf secretory cavities being obscure, smaller and denser; by the midrib, petioles and branchlets being smooth and lacking prominent protruding tubercules, and also by the slightly larger flowers. The name "semotum" meaning "distant, far removed" refers to this species geographic isolation from the New Zealand ngaio (Myoporum laetum). Even more pleasing is that the world expert on the genus Bob Chinnock is delighted by the discovery and fully convinced of the species distinctiveness. It's nice to know that our cautious approach to the Chatham Island Myoporum "problem" has paid off.

As far as we can tell Myoporum semotum is naturally endemic to Pitt Island and the smaller islands that surround it. We have seen and/or collected material from Rabbit, Mangere and South-East Islands and seen images of it from Little Mangere. The new species is inexplicably absent from Chatham Island from where we have only seen New Zealand ngaio and that only from sites suggesting that it is not native to the islands. The formal recognition of Myoporum semotum brings to 37 the total number of endemic ferns and flowering plants now known only from the Chatham Islands. It is noteworthy that the new species is also a rather large tree, demonstrating that new species need not be obscure little herbs and grasses, and that all it takes is a critical eye to find something new on the Chathams. The last such discovery, also first recognised by Peter Heenan was Olearia telmatica (Heenan et al. 2008), although there of course, Chatham Islanders had long recognised its distinctiveness. This makes Myoporum semotum all the more noteworthy, as it seems no one had previously remarked on the possibility of ngaio plants on the Chathams being potentially distinct from New Zealand ones.

Chatham Island ngaio foliage. Pitt Island.  Image: Amanda BairdChatham Island ngaio foliage. Pitt Island. Image: Amanda BairdNot surprisingly for a new species on the Chatham Islands, Myoporum semotum is also a threatened species. Heenan & de Lange (2011) conclude that it merits a conservation listing of "Threatened/Nationally Vulnerable". In their paper they note that the species is in decline on Pitt Island due to habitat deterioration in such places as Waipaua Scenic Reserve. The species is however, secure on the Nature Reserves of Mangere and South-East Islands, though it is hardly common there. Recently Department of Conservation staff have found some reasonable sized populations near Hakepa Hill (known also as "Walkemup") and these may be included within a new covenant being set up by the conservation minded Pitt islanders. More worrying by far though, is the risk of hybridisation with New Zealand ngaio. Ngaio species hybridise readily in New Zealand, where the Tasmanian ngaio (or more correctly boobialla) M. insulare has been widely planted, and as a result has formed extensive hybrid swarms with New Zealand ngaio such that in some places it is now impossible to obtain pure M. laetum plants for restoration plantings and the nursery trade.

The same is likely to happen on the Chatham Islands as well, though so far, more by accident than design, a very conservative planting regime on Mangere Island has avoided mixing up Chatham Island sourced M. laetum with Pitt Island M. semotum. While that's good news, it is very important that people make sure that M. laetum does not reach Pitt Island. In 2008 a survey of Pitt Island gardens by Heenan, I and Pitt Islanders did not find any Myoporum laetum in cultivation on the island. While that's good news, M. laetum is widely cultivated as a shelter belt tree on Chatham Island. As there is no doubt that if M. semotum and M. laetum are planted together they will hybridise, its really important that M. laetum is kept from reaching Pitt Island. The good news is that Myoporum semotum, as a true Chatham Islander is well suited to the islands climate and so just as good, if not a better plant to use for shelter belts. We also like to think it's more attractive than M. laetum - but then we are biased! Perhaps islanders may wish to consider planting only their endemic ngaio instead of the New Zealand one, and - even better - replacing existing M. laetum shelter belts and plantings with M. semotum.

Chatham Island ngaio ([i]Myoporum semotum[/i]) leaf – note minute scarcely discernible secretory cavities. Pitt Island.  Image: Amanda BairdChatham Island ngaio (Myoporum semotum) leaf – note minute scarcely discernible secretory cavities. Pitt Island. Image: Amanda BairdAcknowledgements
I'd like to thank the staff of the Chatham Island area office, in particular Bridget Gibb and Amanda Baird for their support of the plant research being undertaken by myself and Peter Heenan on the Chatham Islands and along with Brian Rance their help in providing live plants, herbarium specimens and images of Myoporum semotum. I also thank Bob Chinnock for his interest in this species, assistance and constructive comments on the paper describing this species and from which this note is derived. As always I remain grateful to the Chatham Island people, and in this particular case the Pitt Islanders for their hospitality, and in granting permission to access their land and collect plant specimens.

References
Allan, H.H. 1961: Flora of New Zealand. Vol. I. Wellington, Government Printer.
APG III. 2009: An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society 161: 105-121.

Chinnock, R.J. 2007: Eremophila and allied genera: a monograph of the plant family Myoporaceae. Kenthurst, Australia, Rosenberg.

Connor, H.E. 1977: The poisonous plants of New Zealand. New Zealand Department of Scientific and Industrial Research Bulletin 99. Wellington, Government Printer.

Heenan, P.B.; de Lange, P.J.; Houliston, G.J.; Barnaud, A.; Murray, B.G. 2008: Olearia telmatica (Asteraceae; Astereae), a new tree species endemic to the Chatham Islands. New Zealand Journal of Botany 46: 567-583.

Heenan, P.B.; Mitchell, A.D.; de Lange, P.J.; Keeling, J.; Paterson, A.D. 2010: Late-Cenozoic origin and diversification of Chatham Islands endemic plant species revealed by analyses of DNA sequence data. New Zealand Journal of Botany 48: 83-136.

Heenan, P.B.; de Lange, P.J. 2011: Myoporum semotum (Scrophulariaceae), a new tree species from the Chatham Islands, New Zealand. New Zealand Journal of Botany 49: 17-26.

Sykes, W.R. 1987: Kermadec ngaio (Myoporum, Myoporaceae). New Zealand Journal of Botany 25: 595-601.