The New Zealand Plant Conservation Network

Species

Pterostylis cernua

Etymology

Pterostylis: winged column
cernua: drooping

Common Name(s)

Westland Greenhood

Current Conservation Status

2012 - At Risk - Naturally Uncommon

Conservation status of New Zealand indigenous vascular plants, 2012
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2012 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2009 and replaces all previous NZTCS lists for vascular plants. Authors: Peter J. de Lange, Jeremy R. Rolfe, Paul D. Champion, Shannel P. Courtney, Peter B. Heenan, John W. Barkla, Ewen K. Cameron, David A. Norton and Rodney A. Hitchmough. File size: 792KB

Previous Conservation Status

2009 - At Risk - Naturally Uncommon
2004 - Sparse

Qualifiers

2012 - Sp
2009 - EF, DP

Authority

Pterostylis cernua D.L.Jones, Molloy et M.A.Clem.

Family

Orchidaceae

Flora Category

Vascular - Native

Structural Class

Orchids

Synonyms

None (first described in 1997)

Distribution

Endemic. South Island, West Coast in and around Hokitika, Kumara and Lake Mahinepua - exact distribution still to be determined as this species was only recognised and described as new in 1997.

Habitat

Lowland (10-40 m a.s.l.) in swampy ground, roadside drains, ditches, margins of peat lakes and fens in sites subject to periodic inundation. Also on poorly drained gley soils overlying infertile, poorly drained gravels stemming from past glacial outwash.

Features

Terrestrial greenhood orchid growing in small colonies of 1-8 plants. Plants dimorphic. Sterile plants 30-60 mm tall, 3-5-leaved; leaves 15-35 x 4-7 mm, dark green to yellow-green, elliptic to elliptic-lanceolate, margins entire or slightly irregular. Flowering plants 60-120 mm tall. Leaves 4-5, 20-65 x 5-7 mm, cauline, erect to spreading; narrowly lanceolate, dark green to yellow-green, sessile, sheathing at base; margins entire; apex acuminate. Pedicel 10-20 mm long, slender. Ovary 9-12 mm, asymmetric, ribbed. Flower solitary, 14-18 mm long, semi-nodding, translucent white and dark green with red-brown suffusions toward galea apex and on lateral sepals; galea erect and gibbous at the base then leaning forwards before decurving in a shallow curve to the apex, the dorsal sepal ovate-lanceolate in outline then flattened, 25-28 x 11-13 mm, expanded in the proximal third then sharply narrowed, gradually tapering to the acuminate apex. Lateral sepals erect, loosely embracing galea, leaving a narrow gap to petal margins; conjoined portion 5-7 x 6-7 mm at top, narrowed to 2 mm wide at base, margins inrolled toward apex and tapered into the free points; free points 13-15 mm long, filiform, curved forwards, tips protruding over galea. Petals 17-20 x 3-4 mm, green with a narrow white central area towards the base, apex reddish-brown; obliquely oblong-lanceolate, falcate, acute, flange vestigial. Labellum erect, curved forwards distally, the apex protruding through the sinus in the set position; lamina 7-8 x 2-2.5 mm, dark green with a black-green central callus, narrowly obovate, apex subobtuse, labellum hinge ligulate 3 x 2 mm. Capsules ellipsoid, deeply grooved, yellow-brown to green-brown prior to dehiscence.

Similar Taxa

When it was described P. cernua was said to be part of the P. montana Hatch complex. However, it has little obvious relationship to entities within that species aggregate and is infact much harder to distinguish from variants within the P. graminea Hook.f. complex. From these it chiefly differs by its somewhat broader and characteristically bunched leaves, and usually smaller (14-18 mm long), distinctly decurved, somewhat nodding narrow (6-7 mm wide) flowers and filiform free points on the lateral sepals. the most widespread form of the P. graminea complex in the South Island prefers drier habitats than P. cernua.

Flowering

November - January

Flower Colours

Green,White

Fruiting

December - April

Propagation Technique

Difficult - should not be removed from the wild. Basic orchid mix consists of 2 parts medium coarse sand, ideally clean river sand; 2 parts soil, humus or leaf-mould; 1 part weathered sawdust or rotting wood; 1 part granulated bark. For Pterostylis shade of 50% and pots kept evenly moist.

Threats

The type locality is under constant threat from road maintenance and widening. Plants at this site are also at risk from weka predation (the birds plough up plants and eat the orchid tubers). Aside from the extreme vulnerability at this site P. cernua seems secure at the other sites in which it has been found. It is intensively monitored at the most of the known populations and more plants and locations are being discovered each season. These results suggest it is a biologically sparse, potentially widespread and easily overlooked plant. The declines happening at the type locality seem the exception rather than the rule for the species.

Chromosome No.

2n = 44

Endemic Taxon

Yes

Endemic Genus

No

Endemic Family

No

This page last updated on 19 May 2014