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Unlikely Place for orchids

9/10/2017

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Greetings fellow Foxies,
I was surprised recently to see orchids in bare and dry bark covered soil under wandoos and powderbarks in Dryandra Woodland Candy Block. Small and relatively inconspicuous Wandoo Beard Orchids and Frog Greenhood Orchids are tough customers that are adapted to drier environments. The Wandoo Beard Orchid (Calochilus stramenicola) has reduced petals and sepals that only partially open and a dense bearded labellum. Calochilus means"sweet lips".They may only open for a day or two while emitting a pheromone to attract large male Scoliid wasps. My colleague Lyn Alcock caught the image of a desperate male wasp attempting to enter a partially opened flower. If the wasp didn’t return the next day, the flower may have pollinated itself and closed.

Not fair! As a fellow male I express solidarity with the poor fellow.
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does the interior resemble a female wasp?
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male wasp desperately attempting to mate
 With these were several tiny but very healthy Frog Greenhood/ Pterostylis sargentii orchids flowering in Foxes lair in August!) and a single blue sun orchid about to open. The Scented Sun Orchid/Thelymitra macrophylla is relatively common in Foxes Lair in mid- late October including some tough places like two that flower in a marri log on the Banksia Walk.
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Frog Greenhood Orchid at Candy Block
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Scented Sun Orchid
South African Orchids are also occasionally found in tough places like that about this time.
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Bird Orchid Pterostylis barbata

24/9/2017

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Greetings fellow Foxies,
 
I was excited to find a Bird Orchid at a Dryandra Woodland reserve on Chomley Road, south-east of Highbury, because I hadn’t seen one for 60 years. My interest in wildflowers began then when my mother and I used to look for orchids in remnant bush at Karrakatta Cemetery. Alas now all graves.
 
This orchid has always fired my imagination with its elegant shape, translucence and the strange wispy labellum that gives the species name. Barbata means beard.
 
A few swipes of the trusty scalpel showed that bird orchids are basically redesigned greenhoods with a wispy labellum.
In this case the hood is folded inwards to form the entry and exit spots for gnats with essentially the same column tube and anther location.
 
I can’t work out how the wisps on the labellum prevent the gnat from escaping out the entry point, but it is hinged like other species to close when activated.
I wonder if the wisps help to spread a pheromone to attract male wasps?
 
Unlike the Jug and Shell orchids there is no little structure at the base of the labellum to trap gnats and retain them for a miserable death
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Shell and Jug Orchids

23/9/2017

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 Greetings fellow Foxies,
 
After dissecting greenhood orchids to see how they trapped insects I moved on to shell and jug orchids that have a more open appearance. In the shell orchid image below one can see that the lower two sepals are upswept rather than being down to form a landing platform, the hood is more open, and the labellum is much skinnier. A few deft slices of my trusty scalpel revealed how this unlikely combination could force an insect to pollinate the flowers. Near the base of the interior the hood petals fold in and the labellum widens to seal the chamber containing the column tube.
In the cross-section below the labellum is closed, but if you picture it leaning forward, imagine a male gnat crawling down it, following the plant-made scent of a female (pheromone).
When the gnat get to the base, the labellum snaps forward, forcing it to climb the column (leaving behind pollen attached its body), through the tube where it gets another dose of pollen, and out of the flower.

Can you see a gnat that was trapped by a curly bit at the base of the labellum? It is the remains of a Fungus Gnat (rather appropriate that it has been consumed by a fungus), whose maggots consume mushrooms, but more of this below.
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Pterostylis hamiltonii Red-veined Shell Orchid
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Arrows show gnat's journey through the flower
The Jug Orchid, Pterostylis recurva has an even more open- looking structure than shell orchids, but it is just a modification of the shell orchid layout.
It has the same infolded petals and thin labellum with widened base and little horns at the top of the column tube to position the labellum when closed.
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Pterostylis recurva Jug Orchid
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Front and side section
Note the gnat trapped by a strange basal labellum structure. I originally thought that the evil looking hook was meant to poke the gnat in the bum if it tried to reverse down the column, but now suspect a more sinister purpose. The hook itself could stop the labellum from snapping too far back, but the fork underneath seems to be designed to trap insects, as does the curved projection in the shell orchid and the big donger in the Frog Greenhood.
An associate doing a PhD on greenhood orchid pollination agreed with me that evolution rarely produces intricate structures like this for no reason, but said that insect deaths may be collateral damage if the plant is successfully pollinated anyway. Is the hook just a fancy counterweight?
In the image below the column is smeared with pollen, so other gnats had been safely through this flower before this poor individual met its end.


However the mouldy gnat in the shell orchid reminded me that orchids require fungi to form a mycorrhiza. IF the mould spores could serve this purpose, this would be a neat way for these orchids to inoculate their seeds.
Who knows?
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Gnat trapped in Jug Orchid
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Gnat remains in Red-veined Shell Orchid
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Plain but Ingenious Greenhood Orchid

21/9/2017

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Greetings fellow Foxies,
Greenhood orchids look plain but they are little marvels of nature, with the flower being an elaborate trap that forces a gnat or mosquito into a chamber where it brushes past the pistil (female bit) and anther (male bit) to pollinate it. The trapdoor is a modified petal called the labellum.
The dorsal (upper) sepal and petals are fused to form the hood containing the column that forms the tube.
The lower (ventral) sepal together make the landing platform in which, a spring loaded petal called the labellum closes the trap when gnat passes over it. 
I dissected a Dark-banded Greenhood Orchid to show how it works. The gnat is attracted to the flower by the promise of a nectar feed and possibly pheromones that smell like a female. When the gnat crosses the labellum it snaps shut against the column. To escape, the gnat climbs up the light-filled hood, through the tube in the column and squeezes past the pollen. Hairs at tube entry stop the gnat moving backwards. Arrows in the image below show the gnat's journey through the flower.

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Picture
The Frog Greenhood Orchid has looks like it has has a club-like labellum, but the club part is actually a counter weight that snaps the labellum closed when the gnat enters
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    Doug Sawkins is a friend of Foxes Lair who once worked for the WA Department of Agriculture

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