#ThreatenedSpecies of the Week: Northampton Midget Greenhood (Pterostylis sinuata)

Northampton Midget Greenhood (Pterostylis sinuata) is listed as Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), and Critically Endangered under the WA Biodiversity Conservation Act 2016.
Photo credit: Interim Recovery Plan for Pterostylis sinuata
Photo credit: Interim Recovery Plan for Pterostylis sinuata

The Northampton Midget Greenhood was discovered in 1978 by Stan Finck, a Victorian orchid enthusiast. It is a small tuberous herb, 5-10 centimetres tall. The flower spike emerges from a basal rosette of leaves and bears between two and twenty pale green ‘greenhood’ flowers. Flowering occurs over a period of approximately three weeks from August to early September, with seed maturing between October and November. Plants are found in clumps or as solitary individuals. As is usual with the genus Pterostylis, plants become dormant after fruiting. Underground tuberoids continue the life cycle after an annual period of dormancy.

The Northampton Midget Greenhood is known from five populations growing in open Melaleuca uncinata and Hakea recurva low scrub over low heath, in winter-wet clay soils over laterite, north-west of Northampton. Plants occur in open, well-lit, moist areas and flower in lower numbers when the density of the vegetation increases.

Very little is known about the biology or ecology of the species, and further research is required. Orchids have specific requirements for both pollination and germination. Pollination in most species of Pterostylis is thought to involve small Diptera, commonly known as fungus gnats. The insects may be attracted to the plant by sex pheromones emitted by the orchid. The orchid does not produce nectar. Once at the flower, insects are trapped by a hinged labellum and can only escape through a small opening at the top of the column. If an insect has come into contact with pollen while visiting another plant, it then transfers pollen to the next plant visited, resulting in fertilisation. Observations suggest that for the Northampton Midget Greenhood most flowering individuals are pollinated naturally and set seed.

Germination and successful establishment of most native orchids is reliant upon a soil-borne fungal symbiont. The specific nature of the mycorrhiza has not been identified for Pterostylis sinuata. Typically Pterostylis are some of the easiest West Australian orchids to germinate. However, the fungi isolated to date from the Northampton Midget Greenhood appears to be atypical and fails to result in seed germination. Further research is required to resolve this problem.

The main threats to the Northampton Midget Greenhood are hydrological changes; weed invasion; water erosion; road, track and firebreak maintenance activities; feral pigs; livestock grazing; inappropriate fire regimes; and chemical drift.

 

Information Source: Government of Australia, Department of Environment and Energy, and Department of Biodiversity, Conservation and Attractions (Florabase).

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