Identifing Sun Orchids (Draft 20, July 2021)

by Robin Garnett & Phil Collier

Thelymitra holmsii
Thelymitra holmsii Bluestar sun-orchid

Sun orchids, Thelymitra species, are generally true to their name and their flowers only open in the morning of warm, still, sunny days. A bushland scene that looked green and brown at 8 a.m. may be studded with little blue Thelymitra flowers by 11 a.m. if the habitat and weather conditions are right. And those opening days are crucial for identification, as their key distinguishing features are found in the centre of their opened flowers.

Thelymitra mucida
Thelymitra mucida
Plum sun-orchid

We were lucky enough to live at Rubicon Sanctuary (now owned by the Tasmanian Land Conservancy) from 2008 until 2018, which is a hot spot for Sun orchids: 21 of Tasmania’s 38 described Thelymitra species are found there. Two of these, the Plum sun-orchid, T. mucida and the Bluestar sun-orchid, T. holmesii, are listed as threatened, although additional species might also be worthy of listing. Living on site meant that we were prepared and ready for those four or five special days in the year when the full spectacle of opened flowers took place.

To help distinguish the Thelymitra taxa at Rubicon Sanctuary, we have developed a written key, a pictorial key and guidelines for the Rubicon Sanctuary Sun orchids. These can be found at:

These materials were developed with reference to the latest published taxonomy. 21 are described species and the 22nd is very distinctive but undescribed. We have also added commentary to some groups where we feel that the published taxonomy or our interpretation is unclear.

Thelymitra polychroma group
Thelymitra polychroma
Rainbow sun-orchid

Our views have changed over time, partly as a result of observing a greater range of specimens, and partly through re-reading species descriptions and matching them to plants on the ground. The keys are specific to Rubicon Sanctuary and not comprehensive for Tasmania, nevertheless we think that many Central North Field Naturalists will find them useful especially in the north-west. The keys are a work-in-progress and we welcome feedback on them.

Page URL: https://www.disjunctnaturalists.com/articles3/identifying-sun-orchids.htm

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