Mayfly orchid

Acianthus caudatus is a terrestrial, perennial, deciduous, sympodial herb with a single thin, egg-shaped to heart-shaped leaf which is dark green on the upper surface and reddish-purple on its lower surface. The leaf is 8–30 mm (0.3–1 in) long, 6–20 mm (0.2–0.8 in) wide and has wavy or minutely toothed edges. There are up to nine dark purplish flowers on a raceme 50–250 mm (2–10 in) high, each flower 30–40 mm (1–2 in) long. The dorsal sepal is erect, expanded near its base, 15–25 mm (0.6–1 in) long and tapers to a fine point. The lateral sepals are a similar shape but shorter, 15–25 mm (0.6–1 in) long and spread apart from each other. The petals are narrow lance-shaped, 3–5 mm (0.1–0.2 in) long, curved and spread apart from each other. The labellum is egg-shaped to wedge-shaped, 5–6 mm (0.20–0.24 in) long and about 3 mm (0.1 in) wide with the tip turned downwards. Flowering occurs from August to October.

Mayfly orchid grows among low shrubs in open forest south of the Manning River in New South Wales, through Victoria to the Eyre Peninsula in South Australia. It is also found in Tasmania.