This month’s entries are an interesting collection as it is probably the first time that all entries are currently in flower. Rosalie Lawrence entered a Pterostylis pedunculata, Ricky Egel (second) Corysanthes despectans, Robert Lawrence (third) Pyrorchis nigricans whilst both Rob Soergel and Claire Chesson (winner) entered Pheladenia deformis. All four are colony forming species.
Both parts of the scientific name for the winning orchid refer to the labellum. Pheladenia meaning false glands which is referring to the calli and deformis meaning departing from the correct shape or mis-shapen.
The labellum plays an important role in pollination; it is the landing platform for the insect. Depending on the process by which the flower is pollinated – or at least attracting the pollinator – this can attempt to mate with the labellum which it has confused for a female of its species (pseudocopulation), or can then feed on the nectar produce. Like many orchids Pheladenia does not produce nectar so the actual attractant for the insect is hard to determine.
The labellum is a distinctive feature of orchids. A modified petal, they are so amazingly varied and complex that botanists often provided detailed descriptions of the features which are present in various combinations, as a means of describing the species. Terms such as lobes, margins, gland/calli, hairs/vestiture/setae, longitudinal ridges, plates, auricles, spurs, papillae etc are used to describe the various features of the labellum.
Some of the features of the labellum of P. deformis are:
- It is stiffly attached to the column, unlike Arachnorchis tentaculata which is hinged and freely moving
- It is tri-lobed meaning that the labellum shape is divided into three distinct sections.
- Unlike Diuris pardina where this feature is easily seen, it is obscured as the outer two lobes are erect and curved in so that it forms a trumpet like appearance with the column.
- The margins or edges of the labellum have fine teeth which are slightly curved inward. The margins of Arachnorchis cardiochila are smooth-edged and curve outward from the ‘throat’ of the labellum
- It has two types of calli, fleshy, non-secreting glands.
- The ones at the base are not as easily seen but they are described as being papillae, e., small, irregular, pimple-like projections or bumps.
- The more obvious ones that give the flower its bearded appearance are elongate and without a swollen head, like the bristles on a brush.
- In contrast, Thelymitra does not have any type of calli, although it should be noted that calli do play an important role in orchid pollination.
- The apex, tip of the labellum, is curved under (recurved to reflexed)
To see some of the variety of labella, Orchids of South Australia (Bates and Weber, 1990) have several drawings detailing the differences on pages 35 to 38, 81, 97, 104 to 106, 114, 119 to 124.
So why spend time looking at details of labella?
It is not important for identifying Pheladenia deformis but it can be a distinguishing feature for other species, for example, the lateral lobes of Diuris maculata are much narrower than D. pardina (Jones, in Harden (ed.) 1993); or the shape of the callus cluster on Chiloglottis which alludes to the species.
Reference:
Bates, R.J & Weber, J.Z. (1990) Orchids of South Australia, Government Printer, Adelaide
Brown, A., et al, (2013) Field Guide to the Orchids of Western Australia. Perth, WA: Simon Neville Publications
Jones DL (1993). Diuris in Harden GJ Flora of New South Wales, Volume 4. University of NSW Press, Sydney.
Jones, D L et al, (2006) Australian Orchid Genera, an information and orchid identification system, interactive CD-ROM
Thank you to Greg Steenbeeke for assistance with this article.
NOSSA 