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Taxonomy of the Orchidaceae

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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.[1] De Jussieu recognized the Orchidaceae as a separate family in his Genera Plantarum (Jussieu) in 1789.[2] Olof Swartz recognized 25 genera in 1800.[3] Louis Claude Richard provided us in 1817 with the descriptive terminology of the orchids.[4] The next step was taken in 1830-1840 by John Lindley, who recognized four subfamilies.[citation needed] 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.[citation needed] 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).[citation needed] Dressler's 1993 book had considerable influence on later work.[5] Genera Orchidacearum was published in 6 volumes over 15 years.[6] It covers all of the orchids, including a description of each genus. It reflects the considerable progress in orchid taxonomy that had been made since 1993. In the 1990s, orchid taxonomy began to be influenced by molecular phylogenetics based on DNA sequences. The first classification that was based on such cladistic analysis of DNA data was published by Chase et alii in 2003.[7]

An update to that classification was published by Chase et alii in 2015.[8] This classification takes a different approach from Genera Orchidacearum, by consolidating many of the tribes and subtribes, and by recognizing very widely circumscribed genera. Orchidaceae has not yet been covered in The Families and Genera of Vascular Plants, tho most of the vascular plant families have by now been covered.

Changes in the taxonomy of orchids are so frequent that it is recommended that the regularly updated World Checklist of Selected Plant Families be consulted for the most current generic and species classifications. Wikispecies (Orchidaceae) closely follows this source with modifications as they become accepted. The Plant List shows lists of genera and species, but no other taxonomic information.

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 1981 in the book The Orchids: Natural History and Classification, was widely accepted by botanists and growers before the publication of Genera Orchidacearum. The initial scheme of 1981 was modified in 1986, twice in 1990, and then again in 1993. This comprehensive classification relies heavily on morphology, especially a few key characters, such as anther configuration and pollinarium structure. Consequently, many of the taxa are not monophyletic.

According to cladistic analyses based on morphological character states or on nucleotide sequences, the orchid family, as well as the five subfamilies within it, are all monophyletic groups. There is a great similarity with the traditional taxonomy, except for the elevation of Vandoideae to the rank of subfamily. In 1993, the relationships between the subfamilies were still unresolved. Compared to previous classifications, more of the tribes and subtribes were monophyletic, but not all of them were supported by subsequent studies. Cladistic analyses, especially those based on molecular methods provide a firmer basis for classification than intuition, and the certainty (or uncertainty) of conclusions can be quantified by measures of statistical support. While our understanding of orchid phylogeny has greatly improved in recent years, the elucidation of orchid relationships is still ongoing.

Furthermore, about 150 species and about a dozen new genera have been described each year since the beginning of the 21st century.

New developments in this taxonomy occur regularly:

  • 1998: Publication of "A phylogenetic analysis of the Orchidaceae: evidence from rbcL nucleotide sequences" by Kenneth M. Cameron in the American Journal of Botany. 1999. In this study, he supports the five primary monophyletic clades (indicated as subfamilies by Dressler) and states that there is no evidence supporting the previously recognized subfamilies Spiranthoideae, Neottioideae, or Vandoideae.[9]
  • 2003: the Angiosperm Phylogeny Group publishes its update of the classification for the orders and families of flowering plants. In this APG III-system, the family Orchidaceae is included in the order Asparagales.[10]
  • 2003: Publication by Chase et al. of a new phylogenetic classification based on recent DNA research [7]

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:

  • Subfamily Apostasioideae: monophyletic - the most basal of the 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): now accepted as nested within a more broadly defined Orchidoideae as the sub-tribe Spiranthinae
  • 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 Vanilloideae: 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.

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

Asparagales
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. ^ Carolus Linnaeus (Carl von Linné). 1753. Species Plantarum, 1st edition, vol. 2, pages 939-954. Holmiae: Impensis Laurentii Salvii (Lars Salvius). (A facsimile with an introduction by William T. Stearn was published by the Ray Society in 1957). (See External links below).
  2. ^ Antoine Laurent de Jussieu. 1789. "ORCHIDEAE" pages 64-66. In: Genera plantarum :secundum ordines naturales disposita,··· (See External links below).
  3. ^ Olof Swartz. 1800. "Afhandling om Orchidernes Slägter och deras Systematiska indelning". Kongliga vetenskaps academiens nya handlingar 21:115-139. (See External links below).
  4. ^ Louis Claude Richard. 1817. De Orchideis Europaeis annotationes. Parisiis, ex typographia A. Belin. (See External links below).
  5. ^ Robert L. Dressler. 1993. Phylogeny and Classification of the Orchid Family. Cambridge University Press. ISBN 978-0-521-45058-4. 314 pages
  6. ^ Alec M. Pridgeon, Phillip J. Cribb, Mark W. Chase, and Finn N. Rasmussen. 1999-2014. Genera Orchidacearum Oxford University Press. ISBN 978-0-19-850513-6 (volume 1), ISBN 978-0-19-850710-9 (volume 2), ISBN 978-0-19-850711-6 (volume 3), ISBN 978-0-19-850712-3 (volume 4), ISBN 978-0-19-850713-0 (volume 5), ISBN 978-0-19-964651-7 (volume 6)
  7. ^ a b Mark W. Chase, Kenneth M. Cameron, Russell L. Barrett, and John V. Freudenstein. 2003. "DNA data and Orchidaceae systematics: a new phylogenetic classification". pages 69-89. In: Kingsley W. Dixon, Shelagh P. Kell, Russell L. Barrett, and Phillip J. Cribb (editors). 2003. Orchid Conservation. Natural History Publications, Kota Kinabalu, Sabah, Malaysia. ISBN 978-983-812-078-4. (See External links below).
  8. ^ Mark W. Chase, Kenneth M. Cameron, John V. Freudenstein, Alec M. Pridgeon, Gerardo A. Salazar, Cássio van den Berg, and André Schuiteman. 2015. "An updated classification of Orchidaceae". Botanical Journal of the Linnean Society 177(2):151-174. (See External links below).
  9. ^ 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
  10. ^ Botanical Journal of the Linnean Society 141: 399-436 (Available online: Abstract | Full text (HTML) | Full text (PDF))

Sources

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