A very “un-orchid like” orchid
In my last blog, I introduced the concept of floral mimicry and left you with the tantalizing question: Who are the models and who are the mimics?
I am pleased to introduce you to Thelymitra, an orchid genus packed full of mimics.
The genus Thelymitra contains terrestrial deciduous orchids that are widespread across Australasia.
Notable features of Thelymitra include a strongly actinomorphic perianth (all the tepals are the same colour and shape) and that the genus lacks distinct labellum ornamentation that so many other orchid genera possess.
It is considered an unusual genus within the Orchidaceae, largely due to the prevalence of this very “un- orchid like” morphology (Dressler 1981).
The distinguishing feature used to characterise between species of Thelymitra relates to the central column structure. The column is produced from the fusion of the style, two staminodes and a single fertile anther.
Most species have flowers that are blue/purple, an unusual colour for terrestrial orchids though a few distinct colour morphs exist such as red and yellow (Jones 2006).
Thelymitra iconically display nastic movements, which has influenced the common name for this genus of ‘Sun Orchids’. The flowers typically open on bright sunny days; the length of time that flowers are open differs between species (Jones 2006).
Thelymitra is a prominent food deceptive genus in the Australian Diuridae and all species are rewardless (Jones 2006). The symmetrical form, together with its lack of reward and close resemblance too many Australian lily-like taxa, suggest that many Thelymitra species are food deceptive mimics of local, co-blooming and pollen rewarding guilds (Bates and Weber 1990).
Dressler RL (1981) Biology of the orchid bees (Euglossini). Annual Review of Ecological Systematics 13, 373 – 394.
Bates RJ, Weber JZ (1990) Orchids of South Australia. (South Australia Government Printer: Adelaide).
Jones DL (2006) “A complete guide to native orchids of Australia, including the island territories‟. (Reed New Holland: Sydney).