Tall Greenhood Orchid - A study of flowers and leaves

Yesterday I went down to one of my favourite haunts along the Belmore Falls Road, to check out the Tall Greenhoods (Bunochilus longifolius) which grow there in abundance. It has been a dry winter in Robertson, and these plants which normally flower much earlier (here) have been somewhat delayed in their flowering. In the Southern Highlands, this species is seen in flower from May onwards, through to September, but these plants are just flowering now, in this location - a normally wet creek bed, within a Melaleuca thicket. It is a densely shaded environment, hence the nearly bare ground. This location is surrounded by ferns, but just here, the ground is open, with deep leaf litter - which is for these Orchids.

Frontal view of the flower - with Labellum "set" (open)
This species may be conveniently compared and contrasted
with the closely related plant Bunochilus umbrinus
recently shown by "Flabmeister" over at "The House of Fran-mart"

Flower as seen from below - with Labellum "set"
The column structure is just visible inside the "hood".
Note also the flanges inside the lower part of the "hood" (galea).
Whaen the Labellum is triggered by an insect (or by movement)
these flanges help seal the lower part of the hood.

Profile view - labellum "set" (open)
Note the yellow block of the pollinia in the front of the "hood".
That is visible through the translucent hood.

The labellum of these plants is movement sensitive.
In this case it has been triggered, and has snapped closed.
You can see the brown, smooth underside of the labellum.
You can also see the position of the pollinia high inside the "hood"
above the column structure at the very front end of the hood.
The lateral sepals are hanging below the flower (deflexed).
A composite image to show the labellum open ("set")
and then closed once triggered.
These images are all of the same flower.

This plant gains its scientific name from the long leaves (of the flowering plants). The flower scape is quite tall - much taller than most Greenhoods - the reason for its "common name".

• The PlantNET site says: "Scape 15–40 cm high, with 5–8 linear to lanceolate spreading stem leaves 3–9 cm long, 3–5 mm wide."
  

The stem leaves tend to grow out to opposite sides of the stem (not located in a loose spiral around the stem, as in some Greenhoods).
By contrast, some non-flowering (immature) plants have rounded rosette leaves. These are small leaves - the whole plant only the size of a 10 cent coin. The graininess of the leaves (see the light reflections) is typical of Greenhoods, and helps distinguish these tiny plants from other small non-Orchid plants. The leaf litter is formed mostly by Melaleuca squarrosa leaves forming a dense mulch on the ground. This image, is about 2.5 times larger than life (about 6 times if clicked to view at full size).Some immature plants have rounded leaves (plants A and B in this image). Others start to develop the long, narrow leaves, but without a flowering stem (plants C, D and E in this image). None of these plants will flower this season.This is not an attempt at an "art shot". Here is an as-yet-unopened bud. It is back lit with a shaft of sunlight streaming through an opening in the canopy of the Melaleuca shrubs. The bright light reveals the internal structure of the flower - the column, which holds the pollinia, clearly visible through the translucent "hood".