Part One covered hints for photographing orchids so as to be able to identify the plant. Part Two gives an example with Cyrtostylis robusta (Winter Gnat Orchid) and C. reniformis (Small Gnat Orchid).
Although the flowering times are different – C reniformis is spring flowering and C. robusta is winter flowering – there is a slight overlap in August when it is possible for both to be flowering at the same time and in the same place.
The flowers are very similar but major difference between the two species is the leaf. Both leaves are roughly kidney shape but C. robusta is pale green with pale , almost undistinguished veins, silvery underneath whilst C. reniformis is heavily veined, blue-green above and green below.
The other differences are more subtle.
C. reniformis has dark buds and the apex of the labellum tends to be rounded rather than pointed
C. robusta has pale reddish buds and larger flowers, labellum crenulated (slightly wavy) and a fine point at the apex.
Consequently, it is important that photographs of the flowers clearly show the labellum – pointed labellum apex for C. robusta compared with the rounded labellum tip of C. reniformis.
Part Two of the November competition consisted of photographs of insects on orchids. There was quite a range of insects but the winner was a draw between Cyrtostylis robusta (Winter Gnat Orchid) with an ant and Pterostylis curta (Blunt Greenhood) with a midge fly; both taken by Doug Castle.
With today’s technology it is not only easier to take crisp images but fine details can be seen particularly when enlarging the image. Hence when the pictures are enlarged it is possible to see hairs on the ant and feathered antennae on the midge fly.
With identifying orchids, it is often the detail that is important. Both of these orchids are distinctive and can be readily identified but it is good to examine why this is the case.
With the greenhood, there is enough detail to see that the dorsal sepal and lateral petals have united to form a galea, ie hood, and that the lateral sepals are semi-fused and erect resulting in lateral orifices (side gap) between the two structures. These are some of the features that separate Pterostylis* from the other greenhoods such as Diplodium, Speculantha and Taurantha. This becomes apparent when browsing through the greenhood photographs, pages 286 to 339, in Jones “A Complete Guide to Native Orchids of Australia”. Having established that the plant is a Pterostylis, the twisted labellum is diagnostic of a P.curta as it is the only one that is described with a twisted labellum. Although not all the identifying features are present, enough information is available in this picture for identification.
In contrast the photograph of the Cyrtostylis robusta only has sufficient data to confidently identify it as a Cyrtostylis species, having a distinctive labellum that is larger than the lateral sepals and petals. In South Australia there are only two species and according to Bates (2011), the distinguishing features between the two
appear to be the leaf, the bud and the labellum. In this picture, the angle of the image does not give a clear view of the labellum (it could possibly be damaged) and of course there is no bud or leaf. It is possible that the pale edges of the dorsal sepal may give a clue to species identification as C. reniformis has mainly darker buds than C. robusta. Obviously Doug was able to identify it from his observations of the other features not present in this photograph.
In summary, one image is not always sufficient for identification. As was discussed on the night, to confirm identification, orchids should always be photographed from more than one angle, including pictures of other parts of the plant.
*In South Australia, Pterostylis foliata is a possible exception as it has no obvious lateral orifice.
Jones, D.L., T. Hopley, S.M. Duffy, K.J. Richards, M.A. Clements & X. Zhang (2006) Australian orchid genera. An information and identification system. CSIRO Publishing: Collingwood, Vic.
Bates, R.J. (2011) South Australia’s Native Orchids. DVD-ROM. Native Orchid Society of South Australia Inc.: Adelaide.
Jones, D.L. (2006) A complete guide to native orchids of Australia, including the island territories. New Holland Publishers: Sydney.