Ramarama, A perspective

This article takes its root from recent visit to “The Meeting of the Waters Reserve” near New Plymouth.It’s a relatively small DOC reserve with remnant forest containing Tawa, Matai, Totara and Kahikatea as its main canopy trees, that line both sides of the Waiwhakaiho river. It is under this canopy where something curious occurs.

The genus Lophomyrtus is endemic to our country and it contains two species. They are Rōhutu (Lophomyrtus obcordata); and Ramarama (Lophomyrtus bullata).

Lophomyrtus bullata

Lophomyrtus obcordata

Initially they were placed under the genus Myrtus but were eventually reclassified in their own genus in 1941.In the early 1900’s there was a debate amongst our most notable botanists that there was a third species: Lophomyrtus ralphii. It was thought that it was closely related to L. bullata, however with smaller leaves and with fewer berries. L. ralphii does not exclusively occur at “The Meeting of the Waters Reserve”, it is here, however that evidence was gathered that concluded that L. ralphii is actually a natural hybridisation between L. bullata and L. obcordata. To this day you can still find both Lophomyrtus parents at the reserve and their hybrids in all their different forms. But this is not where the story ends.

A Lophomyrtus hybrid at “The meeting of the waters reserve” near New Plymouth

Since the arrival of myrtle rust (Austropuccinia psidii) in New Zealand in May 2017,L. bullata has  been found to be very susceptible.In reality the infected hosts that have been found are predominantly found in urban areas,or at least this is what we call it. It is actually New Plymouth nurserymen that have propagated this small hybrid tree (from the “Meeting of the Waters Reserve”) that shows many different leaf shapes and colours to the degree that there are now numerous varieties. It adorns many New Zealand gardens in all its colourful varieties. Actually this small tree has been exported all over the world, and in fact, Lophomyrtus is the main affected host of myrtle rust in Tasmania(Biosecurity Tasmania, 2017).

But how does the future look like for this tree and how will it adapt with the presence of the fungal disease, myrtle rust, and since it’s proven to be so susceptible will we lose Lophomyrtus altogether? Curiously, a very similar incursion happened in 1973, when Poplar rust (MelampsoraSpp) first reached New Zealand. Both are fungal diseases and both arrived here on Trans-Tasman wind currents from Australia. Poplars have a long cultural history in New Zealand where they are planted to control erosion and create shelter. Poplar rust proved to be devastating to some of the cultivars present In New Zealand(A.G. Spiers, 1989). On the bright side; resistant cultivars were identified and propagated.  Poplars continue to be of great asset to the agricultural industry. Furthermore; trees do have the ability to adapt and create resistance to some degree. It is proven, however, that myrtle rust(or at least the strain that is present in NZ) is sexual and not clonal, suggesting that the fungus can adapt to New Zealand hosts and environmental circumstances (McTaggart et al.2017). Also, historically it is proven that a disease will not kill all its hosts in order to survive itself. Hopefully there is natural resistance to Myrtle rust present within the species, that in turn can be propagated.

Figure 2 Symptoms of myrtle rust on Lophomyrtus.

Truthfully Lophomyrtus does not have the grandeur of our Kauri or Pōhutukawa. As a sub-canopy tree it has its niche in our unique ecosystem and it would be sadly missed. How the story will unfold for Lophomyrtus remains to be seen.