Overview
The Banded Greenhood (Pterostylis vittata) is an exquisite and widespread winter-flowering terrestrial orchid native to the temperate woodlands and coastal scrub of southern Australia. Distinctively adorned with translucent green hooded flowers highlighted by prominent horizontal bands of rich reddish-brown or bronze, this multi-flowered species adds elegance to the winter forest floor. Equipped with an irritable, spring-loaded sensitive labellum, it executes a sophisticated insect entrapment strategy to ensure cross-pollination.
Biology and Physical Characteristics
Pterostylis vittata develops a sturdy, upright stem clothed in numerous lanceolate, stem-clasping leaves that become progressively smaller toward the apex. In winter (May to September), the stem produces a loose raceme of two to fifteen nodding hooded flowers. The dorsal sepal and petals fuse into an arched galea marked by distinct, contrasting mahogany-red bands over a translucent emerald-green background. The lateral sepals join below the throat to form a broad pouch, while inside sits an irritable, bifurcated labellum adorned with a dense, tufted basal mound of dark setae.
Behavior and Ecology
The pollination mechanism of the Banded Greenhood relies on male fungus gnats. Attracted by volatile chemical kairomones that simulate female gnat pheromones, the insect lands on the exposed, protruding labellum tip. The slightest touch triggers an instantaneous physiological reflex: the irritable labellum snaps inward and upward, slamming the gnat against the inner column within a fraction of a second. Trapped in the dark, translucent chamber, the gnat crawls upward toward the light, contacting the pollinia and stigma before escaping through a narrow exit pore.
Conservation and Human Impact
Evaluated as Least Concern, Pterostylis vittata is common and well-protected across extensive state forests, regional conservation parks, and national parks in Western and South Australia, including Yalgorup National Park, Coffin Bay National Park, and Grampians National Park. While adaptable to diverse soil types, it is susceptible to widespread habitat clearing and high-density grazing by introduced rabbits and livestock. Preserving dense understory scrub ensures healthy winter populations.
Interesting Factoid
The irritable labellum of the Banded Greenhood acts like a biological mouse-trap; once triggered by a gnat, it remains locked closed for several minutes before slowly resetting to its receptive open position.
Last updated: October 2026