Friday, 12 February 2010

Lord Howe Wonders*



[I've covered most of this topic
previously but as usual, here are the notes from my chat with Simon Marnie that didn't quite run due to technical problems... *'Passion for Plants' postings will also appear on the ABC Sydney website (possibly under 'gardening'), and are generally the gist of my 702AM radio interview on Saturday morning, between 9-10 am.]

I visited Lord Howe Island for the first time last year and saw just a few of the plants that are found only on this 7 million year old, 56 square km, volcanic island. There are 243 native species and varieties, with just over 100 found no where else in the world.

The star attractions are the giant figs and the palms. The four palm species grow naturally here and no where else – i.e. they are endemic to the island – although you’ll find one of them in gardens around the world.

There are three genera, all of them endemic to the island: two have only one species, and the best known, Howea, two. I saw them all on a walk to the top of Mount Gower.Although both Howea species are sometimes called Kentia Palm in the horticultural trade, it’s Howea forsteriana, known on the island as the Thatch Palm, that is more widely grown under this name.

The second species, Howea belmoreana, is called Curly Palm on the island.Three botanists from London – Vincent Savolainen and Matthieu Boulestiex from Imperial College London and Bill Baker form Royal Botanic Gardens in Kew (England) – have been studying these palms in great detail over the last few years.The Thatch (or Kentia) Palm grows from sea level to around 300 m, the Curly Palm starts a little higher (at 50 m) and grows up to 400m. The fact that the ranges of these two closely related species overlap has intrigued botanists for some time.

The London trio found the two palms had diverged from a common ancestor less than one million years ago, on Lord Howe Island. Speciation – the process of a new species being formed – has been what we call ‘sympatric’. This means, as I said above, the two species grow in the same place.

The Thatch Palm flowers on average six weeks before the Curly Palm, which may have been enough to allow them to go their separate ways. However there is enough overlap to allow cross-fertilisation. Hybrids exist on the island and you can see one in the Palm Grove of the Royal Botanic Gardens (if it has survived our flying-fox friends).

Our London colleagues continue to discover curious things about our palms. Both are wind-pollinated, even though most palms are pollinated by insects. And the Thatch Palm includes genetic variants across the island: for example, there is a distinct cluster near Ned’s Beach. These populations may well be in the early stages of becoming new species themselves.

The value of the palms to the island’s ecosystem goes without question, but one local curtly noted that ‘Kentia Palm is good for producing seed to grow more palms, and that’s about it!

I can’t finish without mentioning the figs. There is a form of the Moreton Bay Fig found only on Lord Howe Island called Ficus macrophylla f. collumnaris, or locally, the Banyan. Mature trees have 10 or more trunks, each one starting as an aerial root dangling down from a huge spreading branch. These are impressive trees and the forest just grows up through the largest of them which cover about 1 hectare.

Image: Aerial roots dangling from the Lord Howe Island form of Moreton Bay Fig, on Lord Howe Island

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