''Pterostylis × aenigma'', commonly known as enigmatic greenhood is a species of orchid endemic to Victoria. It has a rosette of leaves and a single green and white flower which leans forward and has a brownish point on the end. It is a rare orchid, occurring at only one site with fewer than 100 individual plants and is thought to be a natural hybrid between two species that grow nearby.

Description

''Pterostylis × aenigma'' has a rosette of between three and eight dark green, fleshy, flat leaves, each leaf long and wide. A single green and white flower is borne on a flowering spike high. The flowers are long, wide and lean forward or "nod". The dorsal sepal and

petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...

s are joined and curve forward forming a hood over the

column A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...

. The dorsal sepal is longer than the petals and has a pointed tip. The tip of the hood is brownish. There is a notch in the sinus between the lateral sepals and a large gap between the lateral sepals and petals. The lateral sepals are olive brown and have thread-like tips long. The labellum protrudes through the sinus and is long, about wide, curved, dark brown and blunt. Flowering occurs between November and December.

Taxonomy and naming

''Pterostylis × aenigma'' was first described in 1993 by David Jones and Mark Clements from a specimen collected near Omeo. The description was published in '' Muelleria''. The authors noted that this species is possibly a hybrid between '' Pterostylis cucullata'' and '' P. furcata'' (later corrected to '' P. falcata''), both of which grow nearby. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

(''aenigma'') means "riddle" or "mystery", referring to the "puzzling origin and distribution of this species".

Distribution and habitat

Enigmatic greenhood grows in moist places near streams in open forest at an altitude of near Omeo.

Conservation

About 50 plants of ''Pterostylis × aenigma'' were known in 2003 but only five were located in 2005. The population occurs in the Alpine National Park but is nevertheless threatened by grazing, weed invasion and site disturbance. The species is classified as "Endangered" by the Victorian Government and as "Endangered" (EN) under the Australian Government Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and a recovery plan has been prepared.

References

{{Taxonbar, from=Q15491600 x aenigma Endemic orchids of Australia Orchids of Victoria (Australia) Plants described in 1993 Interspecific orchid hybrids