Prasophyllum

Orchids in the genus Prasophyllum are terrestrial, perennial, deciduous, sympodial herbs usually with a few inconspicuous, fine roots and a pair of more or less spherical tubers partly covered by a fibrous sheath. Replacement tubers form at the end of short root-like stolons. Leek orchids rarely reproduce by forming "daughter" tubers, relying on their flowers for reproduction. A single onion or leek-like leaf develops near the base of the plant and accounts for the common name of the group. The leaf is long, narrow, hollow, cylindrical and glabrous.[3][4][5][6][7]

The inflorescence is a spike or raceme with a few to many non-resupinate flowers breaking through a thin part of the leaf. The dorsal sepal is wider than two lateral sepals which are often joined. The petals are often curved, shorter and narrower than the sepals. As is usual in orchids, one petal is highly modified as the central labellum, differing markedly from the other petals and sepals. The labellum is positioned above the column and rigidly attached to its base. Its edges are usually wavy and rolled back. The labellum has a callus which consists of a raised, fleshy plate which is usually channelled, with the base forming an inverted basin shape. The sexual parts of the flower are fused to the column which is short and has narrow wings, often with a small lobe at the front. Leek orchids usually flower between late winter and early summer, depending on species, and the fruit that follows flowering is a non-fleshy, dehiscent capsule containing up to 500 seeds.[3][4][5][6][7]

The genus Prasophyllum was first formally described by Robert Brown in 1810 and the description was published in Prodromus Florae Novae Hollandiae.[8][9] Brown described twelve species but did not name a type species, however in 1989, Mark Clements nominated P. australe as the lectotype.[1]

The name Prasophyllum is derived from the Ancient Greek words prason meaning "leek"[10]^: 573 and phyllon meaning "leaf".[10]^: 466

Leek orchids occur in all states of Australia, but not in the Northern Territory. There are 20 named species in Western Australia as well as a further 40 that have been discovered but not as yet described.[4] There are 28 species in Tasmania,[3] about 40 in New South Wales[7] and 15 in South Australia.[11] New Zealand has about 6 species, occurring on both main islands as well as Stewart and Chatham Islands.[5][12] In Western Australia alone, they grow in a range of habitats from the margins of salt lakes, to swamps and dense Karri (Eucalyptus diversicolor) forests.[4]

Prasophyllum species are mycotrophic, requiring symbiotic fungi for seed germination. The main fungus is Ceratobasidium cornigerum.[13][14]

Many Western Australian species only flower after summer fires and in other years only produce leaves. Most flowers are strongly scented, produce nectar and are pollinated by insects but a few appear able to self-pollinated if not visited. They often have flowers similar to grass trees in the genus Xanthorrhoea, flower under similar conditions and are visited by a similar range of insects, suggesting that they mimic grass tree flowers.[4][5]

As at October 2017, about 140 species are recognised by the World Checklist of Selected Plant Families. Eight species described in 2017 are not included on the Checklist yet but are included in the International Plant Names Index. They are P. crassum, P. nitidum, P. roseum, P. rousei, P. stygium, P. sylvicola, P. spadiceum and P. tortilis.[2][15]

• Jones, D.L. & Clements, M.A. (2005). "Miscellaneous nomenclature notes and changes in Australian, New Guinea and New Zealand Orchidaceae". The Orchadian. 15 (1): 41.

• Media related to Prasophyllum at Wikimedia Commons
• West Australian orchids