Overview
The Short-eared Donkey Orchid (Diuris decrementa) is an attractive winter-to-spring flowering terrestrial orchid endemic to the inland clay flats and wandoo woodlands of southwestern Western Australia. Characterized by its golden-yellow flowers marked with intricate brown-maroon blotches and conspicuously abbreviated, ear-like petals, this species forms charming small clumps in seasonally saturated clay soils during the cooler months of the year.
Biology and Physical Characteristics
Diuris decrementa produces a tuft of two or three linear, grass-like basal leaves that measure 10 to 20 centimeters in length. From June to August, a slender, green flowering stem rises up to 35 centimeters high, presenting a loose raceme of two to six brightly colored flowers. The dorsal sepal is rounded and hooded, while the lateral sepals are narrow, greenish-brown, and project downward. The two lateral petals, which resemble donkey ears in other members of the genus, are distinctly reduced in length and held slightly forward. The labellum is three-lobed, bright sulfur yellow with prominent reddish-brown radiating stripes.
Behavior and Ecology
Unlike sexually deceptive spider orchids, Diuris decrementa practices food-deceptive mimicry (Batesian mimicry). Its bright yellow and brown flowers visually imitate sympatric native pea bushes (family Fabaceae, such as Daviesia and Pultenaea) that flower simultaneously across woodland understories. Native halictid and colletid bees foraging for pollen and nectar visit the rewardless donkey orchid blossoms by mistake, inadvertently collecting and transferring pollinia between plants.
Conservation and Human Impact
Although evaluated as Least Concern due to numerous viable populations across crown reserves and national parks, Diuris decrementa has lost substantial historical habitat to agricultural land clearing across the Avon Wheatbelt. Remaining populations in roadside verges face pressures from herbicide drift, road maintenance scraping, and invasion by exotic pasture grasses. Conserving remnant woodland strips and managing seasonal livestock grazing remain critical for long-term population stability.
Interesting Factoid
The specific name ‘decrementa’ derives from the Latin for ‘diminished’ or ‘reduced,’ calling attention to its noticeably shorter donkey-ear petals compared to related species in the genus Diuris.
Last updated: October 2026