Journal Number 97
November 2005

AUSTRALIAN NOTES

Field Trip Report - Potter's Scrub 10 July 05
By Thelma Bridle
(From J.NOSSA Vol.29:7 August 2005)

Winter is greenhood flowering time for terrestrial orchids in South Australia and Potter's Scrub provided a feast of these. Potter's Scrub is part of the Coorong National Park and is situated about 20km west of Meningie. Limestone ridges run NE/SW and orchids grow mainly on the SE facing slopes in sandy soil. Bridal creeper was found to be extremely invasive here and conservation efforts will be made to get some rust spore control at this site.

About 10 years ago Oligochaetochilus (then Pterostylis) arenicola was found in large numbers and monitored at the site for a number of years. Rosettes were still abundant with larger rosettes having obvious developing buds. Part of the area suffered a bushfire in 1994.

The spider Caladenia species here have surprisingly been lumped together as C. australis. Previously NOSSA have recorded C. reticulata and hybrids, C. stellata, C. aff. valida and C. tensa. Some further examination of flowers is required to ascertain species present. A number of leaves were found of Caladenia spp., some with buds developing in the leaf axil. C. latifolia was abundant throughout and some had quite well developed buds.

Five different Diplodium (Pterostylis) species have been recorded at Potter's Scrub. The tall purple coloured D. aff. alatum flowers early. Any flowers for 2005 had either aborted, due no doubt to the earlier drought conditions or been chewed off. There was quite a lot of evidence of animal diggings in the area.

D. erythroconchum, with large reddish-brown hoods and "horns" (lateral sepals) at right angles to the hood, were just coming into flower, whereas D. dolichochilum were in full flower. The flowers of this species were bright red with the sun shining through and the "horns" were pointing forwards. The narrow labellum just pointed through the slightly v-shaped sinus. The large, thick labellum of D. erythroconchum was quite prominent through a more pronounced v-shaped sinus.

A new species to some of us was the D. aff. dolichochilum "Newland Head", which is also known
to grow on Kangaroo Island. It occurred quite commonly at Potter's Scrub. The flower was
narrower than D. dolichochilum, with prominent green veining on the broad, swollen petals.
The large, greeny labellum just reached the slightly notched sinus.

D. robustum was the short mallee form at this site. One very large colony had several groups of flowering plants. With a long flowering season, May - Sept, there were still a number of buds present.

All these Diplodium species had many more non-flowering rosettes than flowering scapes, usually reckoned to be in the ratio 100:1.

Cyrtostylis robusta had large colonies of leaves but far fewer flowers. One smaller colony had variegated leaves, so it would be expected that the buds would develop into paler flowers than normal. The Thelymitra aff. nuda had broad, strap leaves which flopped from mid-way along their length. Leaves for the rare T. epipactoides were not found on this occasion, nor could 12 pairs of eyes locate Linguella (Pterostylis) nana "Hills" type, which has only been recorded once from this site.

Orchids recorded:

Acianthus pusillus (f)(a); Caladenia australis (l/b)(w); C. latifolia (b)(a); Cyrtostylis robusta (f)(a); Diplodium. Aff. alatum "tall purple" (l)(u); D. dolichochilum (f)(w); D. aff. dolichochilum "Newland Head" (f)(w); D. erythroconchum (f/b)(u); D. robustum (f/b)(l); Eriochilus cucullatus (l)(u); Hymenochilus sp. (l); Oligochaetochilus; arenicola (b/l)(a); Microtis arenaria (l)(c); M. sp (l); Pterostylis pedunculata (l); Thelymitra aff. nuda (l)(c).

(f - flower; w - widespread; b - bud; a - abundant; l -leaf; c - common; l - localized; u - uncommon).