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Dwarf Shell Orchid - Pterostylis sp. 'Dwarf Shell'
This is a pretty orchid around 10 cm (4”) in height, with white/brown striped flowers (about 2 cm or 3/4” long), which are noticeably narrow when compared to their length. The identification of this orchid was gleamed from the recent publication of the ‘Orchids of Western Australia’ by Andrew Brown, Pat Dundas, Kingsley Dixon and Stephen Hopper, who are well qualified in Orchidaceae. The large number of undescribed Pterostylis spp. listed on the WA Herbarium FloraBase website do not have sufficient information to make an identification, so without actually viewing herbarium specimens, this orchid book is currently the only alternative and has been extensively used in the preparation of this blog.
There was a small colony of Dwarf Shell Orchids growing in a fine brown sand/clay loam, over a low weathered granite outcrop on the edge of a small playa lake (saltlake). Surrounding this narrow granite based habitat is the much drier mallee vegetation, where the substrate is limestone instead of granite. Water from winter rainfall seeps down the gentle slope to keep this habitat moist for extended periods, thereby providing very good orchid growing conditions (see habitat photo above), which is also shared with Pterostylis sanguinea and P. vittata at this time of year.
Pterostylis sp. 'Dwarf Shell' grows under low shrubs a few metres (20 or so feet) from the dry lake, which is situated to the southeast of Mt Ridley, some 65 km (40 miles) from the coast and Esperance. Flowering is recorded from late June to September, which agrees with my July sighting.