Tuesday, 20 May 2014

Alien gum tree vigorous and vibrant



I'll keep the focus on plants, not the recent vandalism at Melbourne's Royal Botanic Gardens. I couldn't do much better than start with this rainbow-coloured bark. It's not on display in the Gardens, yet, but given how fast the Rainbow Gum grows, if our 'seedlings' survive and continue to thrive we could have some within a year or two. What we have now are three plants just over a year old and already three metres tall. This one is flowering for the first time, after only 13 months...


It started as a seed, sown on 21 February 2013. Nursery horticulturist Dermot Molloy, in an nicely understated email, described it and its siblings as 'vigorous'. The three plants all look quite different. The other two are showing no sign of flowering but one has this lovely red-coloured new growth.


Our fear is that these vigorous seedlings might be as good as it gets. To get our first glimpse of the rainbow colours the seedlings of Eucalyptus deglupta need to survive another Melbourne winter, or two. We did have a sapling in our Rhododendron Garden which survived a few years but succumbed eventually to either possums, frost, drought, or all three.

So where to plant it for best chance of success? It comes from hot and wet climes, so you would think our Tropical Glasshouse would be best. However a few cuttings we tried there a few years back were susceptible to mildew and didn't survive. Given its growth rate and the height of our glasshouse, this would in any case be a temporary residence only. Somewhere like the Fern Gully might be best.

What about at Royal Botanic Gardens Cranbourne you might ask. Wouldn't a picturesque gum tree like this be perfect for our Australian Garden? For 800 or so species of eucalypt - EucalyptusCorymbia or Angophora - that would be true. But not Eucalyptus deglupta.

Although we got our seed from a grower in New South Wales, the original plant grew even further away, in the Philippines. It grows wild in the the Davao Oriental and Surigao de Sur area of north-eastern Mindanao. Which is why it is sometimes called the Mindanao Gum.

It also grows naturally in Papua New Guinea and various Indonesian islands, which is why it is sometimes called the Indonesian Gum (not, I think, the Papua New Guinea Gum*). But not in Australia. There are three other species of Eucalyptus native only outside Australia: Eucalyptus urophylla, Eucalyptus orophila and Eucalyptus wetarensis. They all grow in Timor and nearby Indonesian islands, but not Mindanao or anywhere else in the Philippine (there are an additional four species shared between Australia and Papua New Guinea). The Rainbow or Mindanao Gum is famous as the only eucalypt native to the Northern Hemisphere.

None of the other extra-Australian eucalypts are as pretty in the bark as Rainbow Gum. And none, it seems, grow as quickly. The Rainbow Gum is grown for pulp, paper and timber in various countries in the tropics.


As a naive eucalypt taxonomist (i.e. I know very little) I wondered why it wasn't a Corymbia. My simplistic caricature of a bloodwood is a gum tree with flowers at the end of branches like this.

But then the name Corymbia gives a clue - the flowers are arranged in what is called a 'corymb', which is not only a terminal bunch but one where the flowers all end up in more or less the same plane. The flowers on this Eucalyptus deglupta are rather more scattered.

In a collaborative project with researchers from the University of Melbourne, Bogor Botanic Garden in Indonesia, and Arnold Arboretum in the USA, our Research Manager Frank Udovicic actually knows something about its taxonomic relationships. And what he knows is that things are little uncertain.

Frank and his colleagues are comparing DNA sequences to determine where this species fits among the other 700 species of Eucalyptus, and what its closest relatives are. That might tell us more about the evolution of eucalypts generally, about their past distribution and perhaps interesting things like why and when they became fire adapted. For now though, I can confirm it is nestled safely within the genus Eucalyptus.

That said, the leaves of Eucalyptus deglupta don't smell much like a eucalypt. Dermot says they remind him a little of camphor. To me they smell more like a guava, or just plain 'leafy'. Either way, they don't seem to be full of the oils that make Australian eucalypts so flammable.

For now the three plants grow in large tube pots in our nursery. We'd love to get them out into the public display area, but only if we can be confident they will survive. If we leave it much longer we might have nother problem. Assuming they are as vigorous underground as above, we expect there are already a few roots heading towards London.

Images: The image at the top of the post is from the ZME Science site.
*Post-posting my botanical buddy Jim Croft tells me it is called Kamarere in Papua New Guinea, at least that's what he recalls. Another later, another bb, Alistair Hay, confirms.
**And also post-posting, I can point you to the complete genome of Eucalyptus deglupta, as sequenced by Michael Bayly and team, from the plant we used to have growing in the Royal Botanic Gardens! It says it all really - just a bit hard to understand... 

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