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

 

August 2014 Winning Photograph

08 sm CC Caladenia valida

Claire Chesson’s Arachnorchis valida (common name Robust Spider Orchid) was the winning photograph for August.

The name Arachnorchis valida was not validated until 2002; synonym Caladenia valida. Previously it had been included under Caladenia huegelii (a Western Australian species) and Caladenia reticulata.

A. valida grows in sandy or sand over red clay soil, in sheltered clearings within heathy woodland or mallee but within a very restricted and disjunct distribution on Fleurieu Peninsula and Kangaroo Island in South Australia; and Otway Plain, Victoria. Rated Endangered in South Australia, it is not listed nationally.

Although A. valida shares some similar features with A. reticulata (ie 1 to 2 flowers, clubbed sepals, calli on the labellum) it also has quite distinctive features (see chart below) that help to differentiate between the two as they can sometimes be found growing together.

Comparison of A. valida and A. reticulata

Features

A. valida

A. reticulata

Pollinating wasp Phymatothynnus pygidialis Phymatothynnus victor
Leaf Felted Leaf – dense, short hairsSemi erect Very long silky hairs; purplish at the baseErect
Flower Stem Taller – 40 cm, hairy 30 cm, green & purplish red with long silky hairs
Flower Size Though variable, larger – 7 cm 5 cm
Flower Greenish when first opened fading to white or cream as the flower matures Red-brown
Perianth Stiffly spreading – broad based sepals; backswept petalsNo stripes Dorsal sepal erect; perianth spreading downwardRed stripes
Labellum Can be red but without veining Red with veining

 

NB: November Picture Competition Theme – Orchids and Insects

See the 2014 April Journal for hints of photographing orchid pollinators.

References:

http://www.rbg.vic.gov.au/dbpages/dev/vicflora/index.php/viclist/name/4677 accessed 4th September 2014

Threatened Species Profile Fact Sheet Caladenia valida Department for Environment and Heritage, South Australia

International Plant Name Index – http://www.ipni.org/

Personal communications with Claire Chesson

South Australia’s Native Orchids DVD 2011 Bates

Spider-orchids the Genus Caladenia and it Relatives in Australia CD 2011 Gary Backhouse

 

Australian Orchids & the Doctors they Commemorate Part 14 of 20

Richard Sanders Rogers (1862 – 1942)

An Adelaide physician, doctor-soldier and forensic pathologist who described 82 new orchid species (66 from Australia).

Orchids

Diplodium rogersii (= Pterostylis rogersii) or Curled Tongue Shell Orchid

Prasophyllum rogersii or Marsh Leek Orchid