Caleana, commonly known as duck orchids, is a genus of terrestrial orchids in the family Orchidaceae (order Asparagales), native to Australia and New Zealand. The genus was first formally described in 1810 by Robert Brown in his landmark work Prodromus Florae Novae Hollandiae et Insulae Van Diemen, and was named in honour of the botanical collector George Caley.
Plants are perennial, deciduous, and sympodial, growing from a dark red, oval-shaped tuber. Replacement tubers known as "droppers" form at the ends of long stolon-like roots. Each plant produces a single narrow leaf near the base during the growing season, and a wiry brownish-maroon flowering stem bearing one to a few small, dull-coloured flowers. The flowers are non-resupinate and glabrous, with narrow linear sepals and petals that spread obliquely downward.
The most distinctive feature of Caleana is the modified central petal — the labellum — which is attached to the column by a flexible, sensitive stalk. The labellum is insect-shaped and flask-like, with its narrow tip covered in small black calli or glands that release pheromones mimicking those of a female thynnid wasp. When a male thynnid wasp lands and attempts to mate with the labellum, the stalk snaps downward, pressing the wasp against the column so it picks up or deposits pollinia. This form of pollination by sexual deception is shared with the closely related hammer orchids (Drakaea).
Most species occur in Western Australia, typically in sandy soil near seasonally swampy areas. Caleana major (the large duck orchid) is widespread in eastern Australia, while Caleana minor (the small duck orchid) occurs in both eastern Australia and New Zealand — the only species in the genus to reach New Zealand.
The relationship between Caleana and the closely related genus Paracaleana has been debated; molecular studies published in 2014 suggest the two are congeneric, though the Western Australian Herbarium and several recent field guides to Western Australian orchids continue to recognise Paracaleana as a separate genus.
Etymology
The genus name Caleana honours George Caley (1770–1829), an English botanical collector who gathered plants in New South Wales for Joseph Banks in the early nineteenth century. The genus was formally established in 1810 by Robert Brown, who published the description in Prodromus Florae Novae Hollandiae et Insulae Van Diemen.
Distribution
Duck orchids are found across all Australian states except the Northern Territory, with the greatest diversity in Western Australia. Caleana major is restricted to eastern Australia, growing in woodland, damp heath shrubland, and grassland, sometimes on rocky slopes or gravelly soil. Caleana minor shares this eastern Australian range and also extends to New Zealand — the only Caleana species to do so.
Ecology
Caleana orchids are pollinated exclusively by male thynnid wasps through a mechanism of sexual deception. The labellum emits pheromones that mimic female wasp sex pheromones, luring males to attempt copulation. Contact with the sensitive labellum triggers it to snap against the column, causing the wasp to contact the sticky pollinia. The wasp then carries the pollinia to the next flower, achieving cross-pollination. Western Australian species often grow alongside other thynnid-pollinated orchids including hammer orchids (Drakaea), hare orchids (Leporella), and beak orchids (Pyrorchis).
Taxonomy Notes
The circumscription of Caleana relative to Paracaleana has been debated since at least 1989, when Mark Clements argued that the characters used to separate the two genera are not sufficiently significant. A 2014 molecular study supported treating the two as congeneric. Despite this, the Western Australian Herbarium and several recent field guides to Western Australian orchids continue to recognise Paracaleana as a separate genus. GBIF currently recognises 4 accepted descendants under Caleana.
