March 2016 Winning Photograph

1603 sm JS Arachnorchis sp

We frequently receive entries from Western Australia but this month our entries were from both the west and the east. Allen Jennings entered a Calanthe triplicata (Christmas Orchid) from New South Wales. Pauline Meyer’s was from the west, (Western) Flying Duck Orchid, Paracaleana nigrita. The other entries were South Australian, Jenny Pauley’s recently photographed Leporella fimbriata (Fringed Hare Orchid), Greg Sara’s Thelymitra rubra (Common Pink Sun Orchid) and Judy Sara’s Plumatochilos sp. (Bearded Orchid) and Arachnorchis sp. (Spider Orchid).

The winning photograph was Judy’s Spider Orchid. Obviously it was one of the Green Comb Spider Orchids – A. dilatata complex. Of this group there are about a dozen possibilities. Knowing the location, Mt Boothby, helped to narrow the options with the most likely candidate being Arachnorchis stricta but it wasn’t convincing. It would appear that the tips of the sepals may have been chewed off when in bud.

A distinguishing feature of this species is that there are no clubs or osmophores on the sepals. Other species of this complex have clubs. Another feature is that the dorsal sepal is bent over the column unlike many other green combs which have an erect dorsal sepal. The features that caused doubt were lateral sepals looking droopy instead of being characteristically stiffly held out but dry conditions could cause this. The other was that the labellum did not strictly fit the description of A. stricta but then again it is a variable species.

The conclusion was a possible hybrid but there is no information on the likely parents or that is an atypical A. stricta that may have been damaged in bud.

This is an example of the difficulties that can occur when attempting to identify a plant from one photograph.

Reference:

Personal communications Thelma Bridle (NOSSA Conservation Officer)

Personal communications Bob Bates

Bates, R. J., ed. (2011). South Australian Native Orchids. Electronic version, 2011. NOSSA

Rules of entry:

The subject matter must have something to do with Australian orchids.  Any format is acceptable including Photo shopped images, artwork, etc

How to enter:

Email nossa.enquiries@gmail.com – jpg as large as you are able to send it, preferably A4 ratio for printing

Post: PO Box 565, Unley, 5061

Bring in to the meeting

Spotted Pink Sun Orchid – Beautiful, but Only a Hybrid

This week, a local radio station introduced a segment with the phrase “our rarest sun orchid” and that it was called Thelymitra irregularis or Spotted Pink Sun Orchid.  However it certainly is not our rarest sun orchid.

Thelymitra x irregularis is typically a hybrid pink spotted sun orchid
Thelymitra x irregularis,  Peter Watton, 2009

True, it is not common, but that is partly because it is a hybrid and, correctly speaking, the name should be written as Thelymitra x irregularis (the “x” indicates that it is a hybrid).

For a hybrid to occur, the two parent species need to grow in close proximity, the flowers need to open at the same time that the pollinator is visiting flowers, either to collect or to deposit the pollen and, in the case of self pollinating species, before the individual flower has pollinated itself.

The majority of hybrids are sterile, but occasionally some are fertile.  When hybrids occur the majority will only last a few years before disappearing although sometimes colonies are formed which may last for decades.  Hence, it is not usual to name hybrids, but the more common and recurring ones have been named formally.  T. x irregularis is one of them.

Several species of Thelymitra have been proposed as parent species of Thelymitra x irregularis.  Jeanes & Backhouse (2006) give T. ixioides and T. carnea as parents; Weber & Entwisle (1996) and Jones (2006) suggest T. ixioides and T. carnea and/or T. rubra; Bates & Weber (1990) state that in South Australia the parents are T. ixioides and T. rubra, but T. ixioides and T. carnea in the Eastern states; in contrast, Bates (2011) states that in South Australia it is a hybrid between T. juncifolia and T. rubra.  However, without detailed genetic studies or breeding experiments these all remain suggestions.

Due to the transient nature of hybrids and the conditions needed to produce them, the named hybrids are not common, but since the 1890s specimens of Thelymitra x irregularis have been collected in every decade, which suggest that this hybrid readily occurs.  The 71 specimens held in the Australian herbaria have been collected from four states – which gives a good indication of the distribution but not necessarily the frequency of occurrence.  See Australia’s Virtual Herbarium (AVH) for details.  The AVH lists 12 herbarium records for South Australia with specimens collected from the Adelaide Hills, the Barossa Valley, Kangaroo Island and near Naracoorte.

Thelymitra x irregularis
This Thelymitra x irregularis or Pink Spotted Sun Orchid was photographed by Peter Watton in 2009 near Macclesfield, South Australia

The botanical name “irregularis” refers to the description of the column.  With many sun orchids, it is often necessary to observe the column to distinguish one species from another.  In this instance the top of the column is irregularly toothed.  Retired Aussie has some very good photographs with one in particular showing the column detail.

 

Thanks to Juergan Kellermann, State Herbarium of South Australia for his help with this post.

References

Bates (2011). South Australia’s Native Orchids. DVD-ROM

Bates & Weber (1990). Orchids of South Australia.

Jeanes & Backhouse. Wild Orchids of Victoria, Australia

Jones (2006), Native Orchids of Australia, 2nd edn.

Weber & Entwisle (1996). Thelymitra. In: Flora of Victoria, Vol 3.

Australia’s Virtual Herbarium accessed 24th September 2014