Friday, 10 December 2010

Australian heaths reunited with overseas relatives


When I was taught botany, the Australian heaths were thought to be closely related but quite distinct from those found in the Scottish moors or the South African fynbos. Ours were classified in the family Epacridaceae, theirs in the Ericaceae.

We had most of the world’s Epacridaceae – including things like the local Fuschia Heath (Epacris longifolia) – but only one native Rhododendron and another half a dozen or so species in the Ericaceae family.

OK I was educated in Melbourne, and this was a long, long time ago, but I many of us still think this is true.

As discussed with Simon Marnie a few years back, things are different now. Not only have we doubled the number of native Rhododendron species (from one to two…), but DNA evidence shows that our Australian heaths are embedded within the bigger Ericaceae family.

There was bit of confusion for a while about the name of the new Rhododendron species, but it’s now accepted we have Rhododendron viriosum from high-altitude rocky outcrops around Cape Tribulation, and Rhododendron lochiae (also called for a while Rhododendron notiale, but let's not go there) from similar habitats on the Bellenden-Ker Range. Both are rare, and you can see the former – with its straight rather than curved floral ‘trumpet’ – in the Rare and Threatened Garden at Sydney's Royal Botanic Gardens.

In the new family tree, our native heaths are nestled in with the rhododendrons of China (and those two from Australia), the heaths (Erica) of southern Africa and the heathers (Calluna) of Scotland. Their closest relatives turn out to be the blueberries, a cluster of plants including true blueberries (Vaccinium) from all over the world, and the waxberries (Gaultheria) from Australia, New Zealand and South America.

However all is not lost and we can still retain some national pride. Because the southern heath genera have a common and unique ancestor, they will form a distinct subfamily, called the Styphelioideae (within the family Ericaceae).

If you ever need to separate the ‘epacrids’ from the rest of the family Ericaceae, the leaves usually have parallel veins and the flowers produce as many stamens (the male bits that shed pollen) as petals. There are also some more obscure characters that support the grouping, such as thickenings on leaf epidermal cells and the mechanics of pollen release. And of course there are the genetic similarities.

Image: One of our two Australian species, Rhododendron viriosum, in the Royal Botanic Gardens. *This story is based on one from the Radio Archives (May 2007).

No comments: