Tuesday, 11 August 2015

Illuminating the luma


In Armenia, the luma is a unit of currency worth one tenth of a dram. In Chile, it is a baton or truncheon used by police. In the land of physics, a luma is a measure of brightness of the black and white part of a video image (and represented by the letter 'Y').

Back in plant world Luma is a genus of flowering plants in the well known family Myrtaceae (think gum trees, lilly pillies and bottlebrushes). When the Honorary Consul of Australia for Rio de Janeiro, Ronaldo Veirano, was in Melbourne earlier this year he encouraged me to visit the Arrayanes National Park, near Ariloche in the (northern) Patagonian region of Argentina. The reason? The luma.

He didn't mean money, police weaponry or particularly fine video images. The park, a peninsula into the Nahuel Huapi Lake described as like an island by Ronaldo, is renowned for its forest of Luma (Arrayán, Temu or Chilean Myrtle). You access it by boat, or a 12 km walk or bike ride.

Luma apiculata up to 600 years old, apparently, form thick forests on the peninsula as extending into neighbouring areas. The park was established more than 40 years ago to project this forest, with a boardwalk built to protect the roots of the luma.


The luma is a shrub or small tree up to 20 metres tall, with leaves only a few centimetres long (above) and bark smooth and orange (at top of post), both not unlike a crepe myrtle (Lagerstroemia) is seems. It is said that Walt Disney was inspired by the Arrayán forest to create the scenery for his animated film Bambi.

In Melbourne Gardens we have a fine luma hedge separating Gardens House from the perennial border and the rest of the Royal Botanic Gardens (there is also a nicely trimmed clump near the office buildings in Burnley Gardens). Normally you can't see the bark but at the moment (August) heavy pruning means that's pretty much all you can see! By later spring you should be able to again enjoy this robust alternative to the box hedge and its leaves with their aromatic mytaceous perfume when crushed.


There is a little linguistic confusion even within botany. Amomyrtus luma is not the same as Luma, but the genus name Luma comes reputedly from the Mapuche name for that plant, also in the family Myrtaceae. We do not grow Amomyrtus in the Royal Botanic Gardens but I found a labelled plant at the start of the walk to see the Monkey Puzzle Trees in Huerquehue National Park a little further north than the Luma forest. As you can see, vegetatively it is not world's apart (albeit separated by a rather large ocean) from the hedge in our Gardens.


To confuse things further, Psidium sartorianum, is sometimes given the common name Arrayán. It's a guava, but not a species I've seen growing in Melbourne. As with other species in this genus its berries are edible, as are those of Luma and Amomyrtus

There is a second species of Luma, Luma chequen, from central Chile and naturalised elsewhere in South America. I haven't seen it. All other species assigned to the genus Luma over the years have since been moved elsewhere in the family - the global Plant List includes 37 such names.  I might have seen some of them, but not known.

Images: my own except for the trunks of luma in the Arrayanes National Park which is a photgraph copied from Ten Thousand Trees website and originally from a Flickr page by Konekotichy.

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