Dark pink form of "dusky fingers" Orchid.

I had convinced myself that this orchid must be a different species from the other ones I had recently photographed, in Canberra, Goulburn and locally, in Kangaloon. It is so much darker it has to be different - Surely?

Well, actually - No.
I am talking about Petalochilus fuscatus (Caladenia fuscata).
Here are some 10 flowers on the forest floor - from mid pink, pale pink, to nearly white. (Click to enlarge).

Now let me show you why it is the same species, and what makes it this species, not a Petalochilus carneus (Caladenia carnea), which is what I thought it must be. That has proven not to be the case. Instead, what I have done is inadvertently document the extreme variability of this species.

Pale and mid-pink forms growing together.

This pale form displays beautifully the incurved wings of the labellum
This dark form displays the yellow tips of the labellum
and the dark red stripes across the base of the labellum,
and the two rows of "calli" (glands).

The colour of this particular plant was extraordinarily vibrant, growing in a dark patch of the forest floor. In fact, the environment was so dark, I had to use flash, which has probably made the flower look slightly less vibrant than it actually was.

I always remember a comment by David Attenborough in which he referred to these calli on Orchids like this as "like aircraft landing lights on a runway - for insects". I like that phrase, for it perfectly describes the visual function. But of course, these "calli" are glands, and probably produce scent as well. Same purpose, though - to direct the insect where to go into the flower.

• It must be remembered that the sole function of a flower is to achieve successful pollination, and to set seed. Beauty is entirely secondary, if not accidental.

I had photographed this plant several says ago, but missed the diagnostic feature - the shape and texture of the outer side of the dorsal sepal. So I said yesterday that I needed to go back. So I went back today to find this one flower. I managed that, fortunately.

You can see the dust spots on the flower, following the dust storm yesterday. South Australian dust on a Southern Highlands Orchid. This is "actuality blogging" folks - proof of the date of this photo is in the photo itself.

And here is the image I needed to take.

It shows the "dusky" colour on the outside of the dorsal sepal. I have had to brighten the image, to show the soft brownish colour of the back of the flower. It is the same flower as in the image directly above. Same dust spots.

Here is the close-up of the labellum and the column of Petalochilus fuscatus. Note the golden tips along the edge of the labellum. The tip of the labellum is recurved, which can be seen from the side. These yellow "clubs" on the side of the labellum match with the two lines of "Calli" - also golden yellow.

Note the sides of the labellum are incurved, to protect the centre of the flower.How to tell P. fuscatus from P. carneus?

• P. fuscatus tends to have single flowers (per stem). I have seen some with 2 flowers. P. carneus tends to have up to 5 flowers per stem.
• P. fuscatus has brownish pink exterior of the flower, sometimes with longitudinal stripes of red on the back of the dorsal sepal.
• If no red colour is present, the exterior of the dorsal sepal is brownish and hairy.

• By contrast, P. carneus is referred to as "externally greenish to brownish pink". (Field Guide to the Orchids of the ACT. David Jones with Jean Egan and Tony Wood)
• The labellum lobes (the sides of the flower protecting the "column") are "erect, but incurved" in P. fuscatus. By contrast, in P. carneus the sides are said to be erect, but not incurved.

The least helpful advice which the books offer in separating Petalochilus fuscatus and P. carneus is that P. fuscatus tends to flower several weeks earlier than the other species. If one finds just a few flowers, how does one know which is which?

Sure, if you keep records over years, in the same area, and if it then it falls into a pattern, then you can make an informed guess, based upon flowering times. But as I have just come back from Canberra, which is south from here, but lower, there are contradictory factors there too.

If I find lots of "pink fingers" in flower in a few weeks time, then I may be more confidsent in ascribing a name to those later flowering plants. Maybe. But for a "field guide tip" its not very helpful.