Wednesday, August 04, 2010

Pterostylis sp. (Greenhoods)

From Orchids
Source:  Orchids of Western Australia; Brown, Dundas, Dixon & Hoppper
Photos: M. Taylor

As orchids go, these seem pretty bland, at least as they compare to the beautiful orchids in Asia and even some of the other ground orchids here in Australia.  Yep, GROUND ORCHIDS.  Last year during spring I kept seeing some beautiful flowers growing on long slender stems from the ground.  They looked a lot like orchids to me, but orchids growing from the ground instead of nesting in a tree like they were supposed to?  It turns out that all the orchids here in AU are ground orchids and most are much more spectacular than greenhoods, but greenhoods are blooming now so here they are.

There are 300 species of Pterostylis, most of which are in Australia, with a few in New Zealand, New Guinea, and New Caledonia.  Eighty-two species are endemic to Western Australia and two in particular are common.  The genus is divided up into sections for the greenhoods, shell orchids & snail orchids.

The Banded Greenhood (P. vittata) has an all green flower on which the dorsal sepal and petal are joined together to form a hood overtop the column.  The Dark Banded Greenhood (P. sanguinea) is similar except for darker petals.

Both of these and the other greenhoods have a sensitive "door" formed by the lower sepals that slams shut when a gnat or mosquito lands on it.  The door traps the insect up against the stigma where pollen is collected.  After about a half hour, the door opens again and if the bug has not found an escape it is released to continue about its business and hopefully pollinate another flower.

I tried unsuccessfully to trip the door with a grass leaf, but while I tried one of the flowers opened and a gnat flew out.  I guess it works.

Both of these orchids are common to the bush area of Kings Park in Perth and they prefer to grow beneath our sheok trees (Casurinaceae)


No comments: