Taxonomy of the Orchidaceae

The taxonomy of the Orchidaceae (orchid family) has evolved slowly during the last 250 years, starting with Carolus Linnaeus who in 1753 recognized eight genera. De Jussieu recognized the Orchidaceae as a separate family in 1789. Olof Swartz recognized 25 genera in 1800. Louis Claude Richard provided us in 1817 with the descriptive terminology of the orchids. The next step was taken in 1830-1840 by John Lindley, who recognised four subfamilies. He is generally recognized as the father of orchid taxonomy. The next important step was taken by George Bentham in 1881 with a new classification, recognizing subtribes for the first time. The next great contributors were Pfitzer (1887), Schlechter (1926), Mansfeld (1937), Dressler and Dodson (1960), Garay (1960, 1972), Vermeulen (1966), again Dressler (1981) and Burns-Balogh and Funk (1986). The latest contribution, Genera Orchidacearum (Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. (1999-2009), Oxford: Oxford Univ. Press.) has published Volumes 1-5 with Volume 6 to follow. It is now more accepted to use this re-circumscription, which follows on from Dressler, but with modifications provided by phylogeny. Changes in the taxonomy of orchids are so frequent that it is also recommended that the regularly updated World Checklist of Selected Plant Families is consulted for the most current generic and species classifications. Wikispecies (Orchidaceae) closely follows these two sources with modifications as they become accepted.

History

The following taxonomy follows largely 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 comprehensive classification relies heavily on morphology and a few key characters, such as anther configuration and pollinarium structure and therefore many of the taxa are not monophyletic.

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, some matters are still unresolved. Tribes and sub-tribes, as listed here below, are increasingly becoming monophyletic, as circumscriptions are resolved, but this has resulted in reassignment of taxa. Cladistic and molecular methods give us a firmer basis, but orchid classification is still an ongoing issue, for example, support for the interelationships of the subfamilies is only just emerging. Furthermore, about 150 species and even new genera are still being regularly discovered annually.

New developments in this taxonomy occur regularly:

Taxonomy

The orchid family (Orchidaceae) is subdivided into five subfamilies, and then into tribes, subtribes, alliances (not a classification used in the International Code of Nomenclature for algae, fungi, and plants) and then genera through sub-genera down to the species. Contemporary taxonomy allows for the accepted nomenclature of natural hybrids.

According to Dressler, there are 5 subfamilies, 22 tribes, 70 subtribes, about 850 genera and about 20,000 species in this family.

A distinction between monandrous and other flowers is particularly relevant in the classification of orchids. The monandrous orchids form a clade consisting of the subfamilies Orchidoideae, Vanilloideae, and Epidendroideae. The other subfamilies, Apostasioideae and Cypripedioideae, have at least two stamens.

The following subfamilies are recognized:

Cladistically the interrelationships of these subfamilies can be shown as follows:

Asparagales


Other families in the Asparagales



Orchidaceae

Apostasioideae

Cypripedioideae

Vanilloideae

Epidendroideae

Orchidoideae







Dragon's Mouth Orchid (Arethusa bulbosa)

Subfamily Apostasioideae

The subfamily Apostasioideae belongs to the orchid family (Orchidaceae). It is a clade, but there is bootstrap support that it is a sister to the other orchid subfamilies. A bootstrap is a method for evaluating the statistical importance of positions of different branches in a phylogenetic tree (= a treelike structure giving the evolutionary development of organisms).

The apostasioid orchids are the most primitive orchids, with only two genera. Neuwiedia has 3 fertile, abaxial (= facing away from the stem) anthers, while Apostasia has two fertile abaxial anthers and a filamentous staminode (= a sterile stamen). Plants with mealy or paste-like pollen, which ordinarily are not aggregated into pellets, called pollinia, with two or three fertile long anthers, leaves with stealthing bases, elongated staminodium and labellum similar to the petals.

These primitive features make them, according to some authorities, not true orchids but rather ancestors of modern orchids. However, modern studies (Stern, Cheadle and Thorsch, 1993) point out that the apostasioid orchids are uniquely defined ( = autapomorphous). This makes them unsuitable as models to be the ancestors of the orchids.

Apostasia Blume, included Adactylus Rolfe and Mesodactylis Wall.
Neuwiedia Blume

Subfamily Cypripedioideae

6 genera with about 115 species, mostly terrestrials or lithophytes:

Tribe Cypripedieae

Subtribe Cypripediinae

Cypripedium Lindl., included Arietinum Beck, Calceolaria Heist. ex Fabr., Calceolus Nieuwl., Ciripedium Zumagl., Criogenes Salisb., Fissipes Small, Hypodema Rchb., Sacodon Raf., Schizopedium Salisb., Stimegas Raf.
Lady Slipper orchid (Cypripedium pubescens)

Subtribe Paphiopedilinae

Paphiopedilum Pfitzer, included Cordula Raf. and Menephora Raf.

Tribe Mexipedieae

Subtribe Mexipediinae

Mexipedium V.A.Albert & M.W.Chase

Tribe Phragmipedieae

Subtribe Phragmipediinae

Phragmipedium Rolfe, included Phragmopedilum Pfitzer, Uropedium Lindl.

Tribe Selenipedieae

Subtribe Selenipediinae

Selenipedium Rchb.f.

Others

xPhragmipaphium Hort.

Subfamily Epidendroideae

This is the largest subfamily, having the largest proportion of incest, comprising 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 myco-heterotrophs. 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

Tribe Arethuseae

Over 500 species.

Subtribe Arethusinae

Calopogon sp.
Arethusa L.
x Elearethusa
x Elecalthusa
Eleorchis F.Maek.
x Elepogon

Subtribe Bletiinae

Ancistrochilus Rolfe
Anthogonium Wall. ex Lindl.
Cephalantheropsis Guillaumin
Eriodes Rolfe, included Neotainiopsis Bennet & Raizada, Tainiopsis Schltr.
Hancockia Rolfe
Hexalectris Raf.
Ipsea Lindl.
Mischobulbum Schltr., included Mischobulbon Schltr. (orth. var.)
Nephelaphyllum Blume
Pachystoma Blume, included Apaturia Lindl., Pachychilus Blume and Pachystylis Blume
Alliance Arundina
Arundina Rich.
Alliance Calopogon
Calopogon R.Br., included Cathea Salisb., Helleborine Kuntze
Tuberous Grasspink (Calopogon tuberosus var. tuberosus)
Alliance Calanthe
Acanthephippium Blume, included Acanthophippium Blume (orth. var.)
Bletia Ruiz & Pav., included Anthogyas Raf., Bletiana Raf., Crybe Lindl., Gyas Salisb., Regnellia Barb. Rodr., Thiebautia Colla
Bletilla Rchb.f., included Jimensia Raf., Polytoma Lour. ex Gomes
Calanthe R.Br., included Alismorkis Thouars, Amblyglottis Blume, Aulostylis Schltr., Calanthidum Pfitzer, Centrosia A.Rich., Centrosis Thouars, Cytheris Lindl., Ghiesbreghtia A.Rich. & Galeotti, Limatodes Blume, Paracalanthe Kudô, Preptanthe Rchb.f., Styloglossum Breda, Sylvalismis Thouars
Phaius Lour., included Cyanorchis Thouars, Gastorchis Thouars, Gastrorchis Schltr., Hecabe Raf., Pachyne Salisb., Pesomeria Lindl., Tankervillia Link
Spathoglottis Blume, included Paxtonia Lindl.
Alliance Coelia
Coelia Lindl., included Bothriochilus Lem.
Alliance Chysis
Chysis Lindl., included Thorvaldsenia Liebm.
Alliance Plocoglottis
Plocoglottis Blume
Alliance Tainia
Tainia Blume, included Ania Lindl., Ascotainia Ridl., Mitopetalum Blume

Subtribe Sobraliinae

Sobralia Ruiz & Pav., included Cyathoglottis Poepp. & Endl., Fregea Rchb.f., Lindsayella Ames & C.Schweinf.

Subtribe Thuniinae

Thunia Rchb.f.

Tribe Calypsoeae

Aplectrum (Nutt.) Torr.
Calypso, included Calypsodium Link, Cytherea Salisb., Norna Wahlenb., Orchidium Sw.
Tipularia Nutt., included Anthericlis Raf., Plecturus Raf.

Tribe Cryptarrheneae

Cryptarrhena R.Br., included Orchidofunckia A.Rich. & Galeotti

Tribe Coelogyneae

Over 400 species

Chelyorchis ampliata

Subtribe Adrorhizinae

Adrorhizon Hook.f.

Subtribe Coelogyninae

Coelogyne Lindl., included Bolborchis Lindl., Hologyne Pfitzer, Ptychogyne Pfitzer
Dendrochilum Blume, included Acoridium Nees & Meyen, Platyclinis Benth.
Pleione D.Don

Tribe Epidendreae

Cosmopolitan; largest tribe of this subfamily, with over 8,000 species

Subtribe Glomerinae

Agrostophyllum Blume
Earina Lindl.
Glomera Blume, included Ischnocentrum Schltr.,Sepalosiphon Schltr.

Subtribe Laeliinae: over 1400 species, mostly tropical American epiphytes, in 43 genera. It contains more than 25% (136) of all hybrid genera.

Alliance Isochilus
Hexisea Lindl., included Costaricaea Schltr., Euothonaea Rchb.f.,
Isochilus R.Br.
Alliance Cattleya
Brassavola R.Br., included Eudisanthema Neck. ex Post & Kuntze, Lysimnia Raf., Tulexis Raf.
Broughtonia R.Br., included Cattleyopsis Lem., Laeliopsis Lindl. & Paxton
Cattleya Lindl., included Maelenia Dumort.
Encyclia Hook., included Amblostoma Scheidw., Dinema Lindl., Hormidium (Lindl.) Heynh., Sulpitia Raf.
Laelia Lindl., included Amalia Rchb.
Myrmecophila Rolfe
Rhyncholaelia Schltr.
Schomburgkia Lindl.
Sophronitis Lindl., included Lophoglottis Raf., Sophronia Lindl.
Guarianthe Dressler & W.E. Higgins (2003)
Alliance Barkeria
Barkeria Knowles & Westc.
Caularthron Raf., included Diacrium (Lindl.) Benth.
Alliance Epidendrum
Epidendrum Jacq., included Amphiglottis Salisb., Anacheilium Hoffmanns., Anocheil' Hoffmanns. ex Rchb., Auliza Small, Coilostylis Raf., Didothion Raf.,, Diothonea Lindl., Dothilophis Raf., Doxosma Raf., Epicladium Small, Epidanthus L.O.Williams, Epidendropsis Garay & Dunst., Exophya Raf., Hemiscleria Lindl., Kalopternix Garay & Dunst., Lanium (Lindl.) Benth., Larnandra Raf., Microepidendrum Brieger (nom. inval.), Minicolumna Brieger (nom. inval.), Nanodes Lindl., Neolehmannia Kraenzl., Neowilliamsia Garay, Nyctosma Raf., Phadrosanthus Neck. ex Raf., Physinga Lindl., Pleuranthium Benth., Prosthechea Knowles & Westc., Pseudepidendrum Rchb.f., Seraphyta Fisch. & C.A.Mey., Spathiger Small, Stenoglossum Kunth, Tritelandra Raf.
Alliance Leptotes
Leptotes Lindl.
Alliance Neocogniauxia
Neocogniauxia Schltr.
Dilomilis Raf.
Tomzanonia Nir
Alliance hybrids
Brassocattleya hort.
Brassoepidendrum hort.
Brassolaeliocattleya hort.
Cattleytonia hort.
Epicattleya hort.
Epilaeliocattleya hort.
Hawkinsara hort.
Laeliocatonia hort.
Laeliocattleya hort. ex Rolfe
Otaara hort.
Potinara hort.
Schombocattleya hort.
Sophrocattleya hort.
Sophrolaelia hort.
Sophrolaeliocattleya hort.

Subtribe Meiracyllinae

Meiracyllium Rchb.f.

These species have single leaves, non-pseudobulbous ramicauls, articulated ovary, deciduous from the pedicel.

Tribe Epipogieae

Tribe Gastrodieae

Bamboo Orchid (Arundina graminifolia)

Tribe Malaxideae

Over 900 species

Tribe Neottieae

About 100 species

Tribe Podochileae

Dendrobium Orchid in southern Florida

Tribe Tropidieae

Formerly placed in the subfamily Spiranthoideae

Tribe Xerorchideae

Subfamily Higher Epidendroideae

Formerly called Vandoideae, 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 myco-heterotrophs, 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 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 a unique feature, a sympodial growth habit and two pollinia.

Tribe Vandeae

Over 1,700 species in more than 130 genera; occurs in tropical Asia, Pacific Islands, tropical America, Australia, and Africa.

Nodding Ladies' tresses (Spiranthes cernua)

Tribe Maxillarieae

70 to 80 genera with about 1,000 species; most grow in tropical America as terrestrials or epiphytes, a few are myco-heterotrophs. Most show pseudobulbs, but a few have reedlike stems or thick underground stems. Blooms have four pollinia.

Subfamily Orchidoideae

Cranefly Orchid (Tipularia discolor)

Tribe Diceratosteleae

Tribe Codonorchideae

Tribe Cranichideae

The former subfamily Spiranthoideae is now embedded in the clade Orchidoideae as the tribe Cranichideae (Dressler, 1993). It includes 95 genera and about 1100 species. Species of this polyphyletic tribe occur in all continents (except Antarctica), but mainly in North and South America and tropical Asia. All subtribes are monophyletic.

Tribe Diseae

Tribe Diurideae

About 550 species in 39 genera; mainly Australasia.

Orchis anthropophorum

Tribe Orchideae

This is the largest tribe, containing more than 1,700 species.

Prairie White-Fringed Orchid (Platanthera leucophaea)
Purple Fringeless orchid
(Platanthera peramoena)

Subfamily Vanilloideae

Tribe Pogonieae

Tribe Vanilleae

Not assigned

These two tribes have recently been assigned to a specific subfamily:

Tribe Triphoreae: A primitive tribe consisting of three genera and twenty species has been assigned to Epidendroideae.

Tribe Wullschlaegelieae:only one genus with two species. The tribe has been lost and the genus has now been assigned to sub-family Epidendroideae, tribe Calypsoeae.

References

  1. ↑ K.M. Cameron, M.W. Chase, W.M. Whitten, P.J. Kores, D.C. Jarrell, V.A. Albert, T. Yukawa, H.G. Hills & D.H. Goldman, 1999: A phylogenetic analysis of the Orchidaceae: evidence from rbcL nucleotide sequences
  2. ↑ Botanical Journal of the Linnean Society 141: 399-436 (Available online: Abstract | Full text (HTML) | Full text (PDF))
  3. ↑ M.W. Chase 2005: DNA data and Orchidaceae systematics: A new phylogenetic classification

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