The following taxonomy follows the classification system of Robert Louis Dressler, an orchid specialist and adjunct curator at the Florida Museum of Natural History. This classification, published in the book The Orchids: Natural History and Classification, is widely accepted by botanists and growers. The initial scheme of 1981 has been modified in 1986, twice in 1990. and then again in 1993. This is the most comprehensive classification at the moment. But it relies heavily on morphology and a few key characters, such as anther configuration and pollinarium structure.
According to morphological cladistics and research with rbcL nucleotide sequences, the orchid family, as well as the clades within the family, are a monophyletic group. There is a great similarity with the traditional taxonomy, except for the Vandoideae, but on lower levels, matters are still unresolved. Few tribes, as circumscribed here below, are monophyletic. Cladistic and molecular methods give us a firmer basis, but the classification is still an ongoing issue. There is even no strong support for the interelationships of the subfamilies. Furthermore, about 150 species and even new genera are still being discovered each year.
The orchid family (Orchidaceae) is subdivided in several subfamilies, and then in tribes, subtribes, alliances and then genera.
According to Dressler, there are 5 subfamilies, 22 tribes, 70 subtribes, about 850 genera and about 20,000 species in this family.
The following subfamilies are recognized :
Subfamily Apostasioideae : monophyletic - the most primitive orchids : 3 fertile anthers or two fertile anthers and a filamentous staminode.
Subfamily Cypripedioideae : monophyletic - 2 fertile diandrous anthers, a shield-shaped staminode and a saccate (= pouch-like) lip.
Subfamily Orchidoideae : single, fertile monandrous, basitonic anther.
(Subfamily Spiranthoideae) : nested within a more broadly defined Orchidoideae
Subfamily Epidendroideae : includes almost 80 % of the orchid species; monophyletic; orchids with an incumbent to suberect ( = ascending towards the edges) anther.
(Subfamily Higher Epidendroideae (formerly Vandoideae) : specialised clade within a more broadly defined Epidendroideae
Subfamily Vanniloideae : an ancient clade now recognized as a distinct subfamily. But, from a molecular point of view, it is rather a sister to subfamily Epidendroideae + subfamily Orchidoideae. This subfamily is a branch at the basal dichotomy of the monandrous orchids.
As the Genera Orchidacearum (Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F.; Oxford Univ. Press.) will only be completed in 2006-2007, and changes in taxonomy of orchids are so frequent, the following taxonomy still follows largely the system of Robert Louis Dressler.
Tribe CRANICHIDEAE : The former subfamily SPIRANTHOIDEAE is now embedded in the clade Orchideoideae as the tribe Cranichideae..
Species of this polyphyletic tribe occur in North and South America; all subtribes are monophyletic.
Subtribe :CRANICHIDINAE
Alliance : PRESCOTTI
Genera : Altensteinia, Cranichis, Ponthieva, Prescottia
Subtribe GOODYERINAE
Alliance GOODYERA
Genera : Goodyera, Ludisia, Platythelys
Alliance : PONTHIEVA
Genera : Baskervilla, Cranichis; Ponthieva
Subtribe PACHYPLECTRONINAE
Genera : Pachyplectron
Subtribe PRESCOTTIINAE
Genera : Altensteinia
Subtribe SPIRANTHINAE
Genera : Aphyllorchis, Spiranthes
Subtribe : MANNIELLINAE
Genera :Manniella
Tribe DICERATOSTELEAE
Genera : Diceratostele
Tribe TROPIDEAE
Genera : Tropidia
Tribe ERYTHRODEAE : All species in this tribe occur in Asia, Africa, and Australia.
Alliance ANOECTOCHILUS
Genera : Anoectochilus, Zeuxine
The following tribes of this subfamily contains some 2,800 species. occurring in the temperate climates of Europe, Africa, and Australia. The species are mainly terrestrial plants with slender stems, spiraling leaves, and mealy pollen. They all have a unique thickened root-stem tuberoid storage organ.
This is the largest subfamily. It comprises more than 10,000 species in about 90 to 100 genera. Most are tropical epiphytes (usually with pseudobulbs), but some are terrestrials and even a few saprophytes. All show a unique development of the single anther : it is incumbent forming a right angle with the column axis or pointed backward in many genera. Most have hard pollinia, i.e. a mass of waxy pollen or of coherent pollen grains; pollinia with caudicle and viscidium or without; stigma entire or 3-lobed; rostellum present; 1-locular ovary; leaves : distichous or spiraling
This is the second largest subfamily with over 300 genera in more than 5,000 species. They are mostly epiphytes, but include some terrestrials and saprophytes, all occurring in most tropical areas. The main stem grows in a single direction. Many of the species develop pseudobulbs (i.e. a bulge at the base of a stem), that are normally shorter and sturdier than those in the epidendroids. The striking characteristics of the vandoids are a cellular pollinium stalk (= stipe), superposed pollinia and the unique development of the incumbent anther, that bends early in development.
Tribe POLYSTACHYEAE : about 200 species which all show four pollinia. The lip often has mealy hairs called pseudopollen on the upper surface.
Genera : Polystachya
Tribe VANDEAE : over 1,700 species in more than 130 genera; occurs in tropical Asia, Pacific Islands, Australia, and Africa.
Subtribe SARCANTHINAE : more than 1,000 species in over 100 genera, including about 208 (38%) hybrid genera; occurs mostly in Asia with a few in Africa.
Tribe MAXILLARIEAE : 70 to 80 genera with about 1,000species; most grow in tropical America as terrestrials or epiphytes, a few are saprophytes. Most show pseudobulbs, but a few have reedlike stems or thick underground stems. Blooms have four pollinia.
Subtribe CORALLORHIZINAE : all saprophytes.
Genera : Aplectrum, Corallorhiza
Subtribe ZYGOPETILINAE : about 150 species. Most exhibited hybrids are to be found in this subtribe.
Genera : Anguloa, Bifrenaria, Lycaste, Neomoorea, Rudolfiella, Teuscheria, Xylobium.
Subtribe MAXILLARIINAE : largest subtribe with nearly half of the tribe species. The leathery leaves are conduplicate, i.e. folded together lengthwise.
Genera : Chrysocycnis, Cyrtidium, Maxillaria, Mormolyca, Pityphyllum, Scuticaria, Sepalosaccus, Trigonidium.
Subtribe DICHAEINAE
Genera : Dichaea
Subtribe TELIPOGONINAE
Genera : Telipogon, Trichoceros
Subtribe : ORNITHOCEPHALINAE
Genera : Ornithocephalus, Zygostates
Tribe CYMBIDIEAE : about 1,800 species in 100 to 130 genera. Species are either terrestrial or epiphytic, and range throughout global tropical regions. All species have, as an unique feature, a sympodial growth habit and two pollinia.
Subtribe CYRTOPODIINAE : over 400 species, usually terrestrial; Asia, Africa, and tropical America.
Subtribe ONCIDIINAE : Largest subtribe with nearly 1,000 species within about 56 to 78 genera, found in tropical America, the Caribbean and Florida. Most are epiphytes, but a few are terrestrials. .They usually have short and stout pseudobulbs.
Alliance ONCIDIUM : largest alliance; includes the majority of genera in cultivation.
Two genera with about 16 species. These rare orchids have two or three lateral anthers. Several primitive features makes them, according to some authorities, not true orchids but rather ancestors of modern orchids.
Genera : Apostasia, Neuwiedia
Subfamily CYPRIPEDIOIDEAE
Four or five genera with about 115 species, mostly terrestrials or lithophytes. They lack pseudobulbs and show a unique shieldlike staminode and pouchlike lip.
These two tribes are not currently assigned to a specific subfamily
Tribe TRIPHOREAE : A primitive tribe consisting of three genera and twenty species. Possibly belongs to the Epidendrum subfamily.
Genera : Monophyllorchis, Triphora
Tribe WULLSCHLAEGELIEAE : only one genus with two species.
Genus : Wullschlaegelia
Reference
Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (1999). Genera Orchidacearum 1. Oxford Univ. Press.
Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (2001). Genera Orchidacearum 2. Oxford Univ. Press.
Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (2003). Genera Orchidacearum 3. Oxford Univ. Press.
Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (to be published in 2005). Genera Orchidacearum 4. Oxford Univ. Press.
The Orchids: Natural History and Classification by Robert L. Dressler – Harvard University Press, 1981 ISBN 0-674-87525-7 -- It is the best popular scientific account of the orchids, their biology, evolution, and classification.
Dressler, Robert L. 1993. Phylogeny and classification of the orchid family. Dioscorides Press, Portland, OR. 314 p.
CHASE, M. W., J. V. FREUDENSTEIN, AND K. M. CAMERON. 2001. DNA data and Orchidaceae systematics: A new phylogenetic classification.
