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
NOSSA 