The Species Orchid Society of Western Australia (Inc)

Ron Heberle's Pterostylis

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Pterostylis (meaning winged style) Greenhood complex.


Other common names are Shell, Snail, Midget, Jug, Cockatoo, Banded, Dwarf,…etc.
The genus is widespread throughout Australia and most abundant in the southern areas.
Their underground vegetative reproduction produces masses of over lapping leaf rosettes, which are mostly immature plants of which about 10%, flower each year.
The flowering plants do not produce rosettes but have varying sized and numbers of cauline leaves.
The highly successful pollinating strategy produces copious seeds that germinate readily and produce large numbers of plants.
Darwin, in his classic work "THE FERTILISATION OF ORCHIDS", stated that Pterostylis had evolved the most amazing and effective reproduction strategy within the world's Orchidaceae.
The first research relating to these strategies was undertaken by Cheeseman in 1833 in New Zealand and this was followed by Fitzgerald 1882; Edith Coleman in the Eastern States and Sargent in 1907 in WA. All were able to define the remarkable mechanism of the sensitive labellum that was able to trap visiting insects.
The insects enter the galea (pouch) and probe the base of the pouch for a liquid they find irresistible. This activates the sensitive labellum, which with the assistance of the column and the column wings forces, the insect backwards and traps it in a confined space. The margins of the column are coated in coarse hairs and notches ensuring that the only way out is upwards. The column wings channel the insect to the sticky stigma and the two pollen sacks. A daub of this sticky glue fastens the pollinia to the insect and they are then transported to the next flower.
The insect attracting agent is a sublime secretion at the base of the pouch and some researchers have postulated that the insects receive a drink/food with possible sexual attractions.
The galea encloses the winged column and sensitive labellum where the dorsal sepals and petals and the lateral sepals unite to form the pouch. The labellum, broadly elliptical, has hairs and indentations along both sides giving footholds to enable the insect to escape upwards. It is held forward below the sinus (the union of the lateral sepals) by an elastic claw at the base. Insects entering trigger off the sensitive labellum that forces the visitor to a confined space where the only escape is upwards so that the pollinating process described earlier is effected. If pollination has not been effected then the labellum retracts ready to repeat the process. This takes from 20 minutes to some hours depending on the ambient temperature.
The precise explanation of just how the elastic claw performs its purpose is still subject to scientific research.
However the mechanism seems to be highly efficient as almost all flowers produce seed capsules.

Pterostylis barbata complex;

The Bird Orchids


This distinctive group is present in most of the lower southwest with only a few outside this area.
The actual number of species is not known but this should be rectified when the current revision is published.
The species name' barbata' refers to the hairy bearded labellum that is characteristic.
The labellum is thin, wiry and has mostly coarse irregular hairs that serve to close off the orifice containing the stigma and pollinias. The same sensitive elastic hinge, as for the entire genus, is employed.

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