May’s theme was miniscule, or less than 10mm. Of the eight entries five were Corunastylis, two Spider orchids from Western Australia and one an epiphyte. The flowers of the two spiders, Caladenia pachychila (photographer Rob & Jenny Pauley) and Caladenia bryceana subsp. bryceana (Pauline Myers) were the largest of the group being about 10mm across whilst the Bulbophylum globuliforme (Ros Miller) and C. despectans (Rosalie Lawrence) were the smallest being only 2mm across.
Of the remaining Corunastyllis entries the flower size ranged from 3mm for C. pumila (Rob & Jenny Pauley), 4mm for C. tepperi (Ricky Egel), 7mm for C. ciliata (Rosalie Lawrence) and 8mm for C. morrisii (Rob & Jenny Pauley).
The winning picture C. morrisii (Bearded or Hairy Midge Orchid) is one of the larger midge orchids. Other synonyms are Prasophyllum morrisii and Genoplesium morrisii. This common species is mainly found in Victoria but it does extend into southern New South Wales in the east and in the west just spills 50 km over the border into South Australia where it is rated endangered. It also occurs in the south east of Tasmania.
Flowering Times: Nov – May
With such a wide distribution range, it is not surprising to see quite a variation in flowering time from late spring through to autumn depending upon location.
Think of deserts and the image is that of a bleak barren landscape with little to see but this is not so. The conditions are harsh but there is a myriad, though not an abundance, of hardy fauna and flora if one but looks closely.
But concerning orchids – No orchids have been found in true deserts….. They also appear to be absent from the arid mountains of the far north-west, or at least no-one has ever found orchids there.
Orchids need moisture and so they do not grow on unstable soils such as dry sand-hills, gibber plains or the many saline areas of the far north but on the desert fringes there are micro-climates where the moisture, humidity and soil structure is just right (to quote Goldilocks) for orchids. This micro-climate is created by [s]hrubland [which] is … [an] … important dryland orchid habitat. Besides providing shade and shelter for the orchids, shrubs like the many species of wattles, Acacia and hop-bush Dodonea drop fine leaves which help to hold the soil together and slowly break down into humus rich with nutrient and water storing capability. These shrublands usually form in soils too dry or shallow for trees. Orchids of course have no need for deep soils as they are shallow rooted.
Of the five desert botanical regions, the Eastern region contains the most number of species with over a dozen species.
Orchids of the Eastern Region – this region is from the east of the Flinders Ranges to the New South Wales border and includes the Olary Spur and Lake Frome.
Arachnorchis toxochila – Dry Land Spider Orchid or Bow Lip Spider Orchid.
Corunastylis tepperi – Mallee Midge Orchid
Diplodium robustum – Common green shell-orchid.
Hymenochilus pagophilus – Mountain Shell-orchid
Microtis eremaea – Desert onion orchid
Microtis frutetorum – Common woodland onion orchid.
Oligochaetochilus bisetus species complex, Rusty rufous-hoods
Oligochaetochilus sp. Blue-bush Plain – Blue Bush rufous-hood (O. bisetus complex)
The Gairdner-Torrens region includes, besides the salt lakes it is named after, the Gawler Ranges and the southern part of the Great Victoria Desert. Though not as many species as the Eastern region, it contains some different species including a Sun Orchid.
The final two regions Lake Eyre and North-Western contain the vast expanses of desert of the far north of South Australia. Definitely not a place to find orchids yet one specimen has been collected from each of these two regions.
Oligochaetochilus sp. Everard Range (L. Scott 173), Mimili Orchid (possibly O. woollsii complex) from North-Western Region.
Oligochaetochilus sp. Gammon Range (O excelusus complex) from the Lake Eyre region.
It is unusual to find orchids in the desert because they only grow when there have been good winter rains which isn’t very often. But nevertheless, here in South Australia we have over 20 possible species – an astonishingly high number for such a harsh area!
Bates R J ed, South Australia’s Native Orchids, 2011 Native Orchid Society of South Australia
Map adapted from Flora of South Australia, Fourth Edition, 1986
The title of this article refers of course to mallee midge orchids of the genus Corunastylis which have been poorly understood.
Summer and autumn 2011 saw good rains across the Murray Mallee from Pinnaroo to Renmark and thus NOSSA members took the opportunity to study mallee midge orchids in flower in March and April. The results are summarised here.
To match species to habitat.
To assess the distribution and population of each species.
To take images of all species.
Midges were found all the way up to Chowilla sand hills, which are just north of the River Murray. Almost every patch of mallee eucalypts seemed to have some Corunastylis species but an understanding of their ecology was needed to find the flowers. Degraded or weedy mallee did not have any midge orchids, nor was hard clay, loose white sand, bare trampled soil or dense ground cover worth searching as midges are very small plants and easily crushed, covered up or sand blasted.
Flowering plants were found mostly in the leaf litter under mature mallee, often with associated patches of native pine or circles of Triodia sp. (porcupine grass). Areas with extra water run off and disturbed soil along road corridors seemed to have produced localised population explosions. A 4WD vehicle proved handy for reaching remote corners of larger parks like Billiat Conservation Park near Alawoona.
The most common species was the red and green flowered mallee midge Corunastylistepperi while the similar but purplish Corunastylis sp. Intermediate came in second. Next came the black midge orchid C. nigricans which seemed to have finished in early March and were found mostly in capsule.
Species of the Corunastylisrufa complex were mostly found in the southern fringes of the mallee. Their classification is ambiguous seeing Australian orchid expert D.L. Jones says Corunastylis rufa is confined to NSW. The un-named species of the complex seen included Corunastylis sp. Dark midge and Corunastylis sp. Narrow segments.
In any case, no fringed labellum species of any kind were observed, so all mallee midges belong to the C. nigricans and C. rufa complexes.
Tiny fruit flies of several species were seen working the flowers but we could not tell if each midge orchid attracted a different fly as the flies are too small to compare! I suspected that specificity of pollinators is low as apparent hybrid midge orchids were noted.
Recognising the different mallee midge orchids:
If the flowers are bright green and the labellum is rounded, deep purple or maroon then it will be C. tepperi, also known as C. fuscoviride. The latter is a better name as it means bright dark and green. C. tepperi has a narrow spike of many tiny flowers. The finished flowers and capsules will take on a yellowish look.
If the labellum is rounded and the flowers are mottled brown to wholly purple-brown, except for white or white striped petals, the species is C. sp. Intermediate.
DNA studies may be required to check the species limits of the many taxa found.
It is doubtful that such a good display will be found next autumn!
Many thanks to NOSSA members who sent me images of mallee midges recently, especially June Niejalke.