Diverse Stirling Range orchids right on the money

On average, if you wander around identifying plant species, one in every dozen will be an orchid. Many species will be more common than orchids and in some regions of the world you might not find a single orchid, at least out of season, but we share this planet with a remarkable variety of orchids. This is just one of the Australian sun orchids, called Queen of Sheba.

Of Australia's 800 or so species, more than 120 grow naturally in the Stirling Ranges in south-western Western Australia, where I spent a few days looking for freshwater red algae (my research obsession) and checking out attractive flowers on the way. In that mountain range, the percentage of orchids is bang on 8% of the flora, as it is worldwide (a whopping 25,000 of the plant species alive today - 300,000 - are in the family Orchidaceae, the biggest plant family by far).

These next pictures are of spider orchids, specially adapted to attract.copulating male wasps as pollinators.

On a fresh August morning, Brian ('Bully') Bilding from Stirling Range Retreat, showed me around 25 species of orchid in just over three hours. Not bad for a group of plants that flower seasonally and spend most of their time reduced to a tuber below the ground. I'd scratched around the afternoon before, finding half a dozen of these. It definitely helps to know your neighbourhood.

To be fair Western Australia is the place to go if you want to see a large chunk of most of this country's floral diversity. While I was there in August the Western Australian Herbarium added the 10,000th published addition to the State's native plant census (FloraBase). There are many more to be described with the total flora currently estimated at 12,437 - that includes known species yet to be described but not plants assumed to be out there but yet to be discovered.

If you look at the total flora of Australia, with around 25,000 species, Western Australia has about half and most of these are in the south-west. To look at it another way, the native flora of the Stirling Range (1,200 square kilometres; 1,500 species) has more plant diversity than the entire United Kingdom (244,000 square kilometres; 1,400 species - although some might quibble about adding migrants since the sixteenth century).

These last three are greenhood orchids, with triggering mechanisms that dump sticky clumps of pollen onto visiting insects.

In total Western Australia boasts about 430 orchid species, compared to the 350 or so in Victoria, the next richest State I would suspect. Lest you protest about the size of WA, I reckon the vast majority of the species grow in the south-west corner, an area smaller than Victoria. And another 17 species of spider orchid (more or less in the genus Caladenia) were freshly described from the South-West this year!

A recent phylogeny (the tree of life, showing how each species is connected to its closest relative with a shared ancestor) of the Orchidaceae showed that the evolution of a 'pollinia' - those sticky clumps of pollen - evolved at least 64 million years into their 112 year old history as group distinct from other plants. Those lineages with pollinia diversified quicker than those without - intricate one-on-one battles with insects loomed, such as the one I described in the Star of Bethlehem Orchid from Madagascar.

Another major step, by 35 million years ago, was heading up into the trees. Like bromeliads, succulents and various other plants surviving in dry habitats, orchids also developed a special form of photosynthesis (using energy from sunlight to convert water and carbon dioxide into oxygen and sugars) called Crassulacean Acid Metabalism (or CAM for short; I will blog about it, one day...).

A final step towards 'world domination' was heading up into the mountains, sometimes in trees, sometimes not. (As yet the production of insect-attracting scents - pheromones - cannot be implicated in diversification - but scientists expect there has to be a sniff of this somewhere in the phylogenetic tree.)

As if to confound all this, about three-quarters of all Australian orchids are ground or terrestrial orchids and the vast majority live in the lowlands or mildly hilly country. Perhaps as with much else in the Australian flora simply isolation and time has resulted in plenty of charming species to photograph. Such as this Blue Beard which, unlike all the other species, also occurs in Victoria.

Images are all orchids from the Stirling Range, photographed on 24 August 2015 (it was hard to leave any out but the out-of-focus-due-to-wind images excluded themselves.) My stab at their names, being a foreigner to these parts, is, from top of post: Thelymitra variegata (Southern Queen of Sheba), Caladenia plicata (Crab-lip Spider Orchid), Caladenia longicaudata (White Spider Orchid), Caladenia flava (Cowslip Orchid), Pterostylis recurva (Jug Orchid), Pterostylis barbata (Bird Orchid), Pterostylis concava (Cupped Banded Greenhood) and Pheladenia (previously Caladenia then Cyanicula) deformis (Blue Beard).


Dan Murphy said…
Is that a sneaky Drosera in the background of the last photo Tim?
Tim Entwisle said…
Yep. Something like D. macrantha I presume. There were some spectacular sundews around!