Thursday, July 19, 2012

The Early Orchids are Out

Blunt Greenhood
Pterostylis curta

These little chaps are just beginning to flower in the Goomburra National Park.

There are several different local species of greenhood. This one can be identified by the rather short “horns”, (actually the tips of two of its sepals).  “Curta” means short. However, the best identifying characteristic is the labellum, which has a sideways twist.

The labellum is a little petal, different from the other green ones, which pokes out of the flower’s “mouth”  like a tongue.

You may notice, as you examine a flower closely, that the labellum suddenly flicks back inside.

What it’s doing is showing you its quick reflexes. If there had been a potential pollinator  on that labellum, the orchid would have flicked its little visitor back against its style. After holding it prisoner for 30-90 minutes,  the labellum would have relaxed as it began to reset. The little gnat would then struggle up towards the light coming in the orchid’s translucent hood. As it did this, using the tiny hairs on the labellum as footholds, a little bundle of pollen would have stick to its back, ready to pollinate the next greenhood that it found itself struggling out of!
The insect pollinators are thought to be all males, and may be attracted into the flower by a “perfume” resembling female gnats’ pheremones.
The labellum usually takes 2-3 hours to reset, but is faster on warm days, and can take all day if it’s cold.
Greenhoods are deciduous orchids. This means that for more than half the year they consist of nothing but an underground tuber. In winter they use up the food stored there, to grow a little rosette of leaves. In a poor year this might be all they can manage, and there is no flower. Food manufactured in the leaf (by photosynthesis) is then used to grow a new tuber to help the plant survive the next year. In a good year (with plenty of sunlight and water for photosynthesis), colony-forming greenhood species like this one also grow several new tubers, each one becoming a new plant.

Just at present, the colonies are showing some flowers and plenty of buds, so it’s a good time to look for them. Their favourite situation is on well-drained slopes and cuttings, with a south-easterly aspect.

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