Tag: Murray

R.J. Bates May 2011

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.

Aims:

1. To match species to habitat.
2. To assess the distribution and population of each species.
3. 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 Corunastylis tepperi 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 Corunastylis rufa 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:

1. 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.
2. 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.