AFRICAN

ORCHIDS

Taxonomy of the Orchidaceae

Description:

The taxonomy of the orchid family has evolved slowly during the last 150 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 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 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.

The orchid family (Orchidaceae) is subdivided in several subfamilies, and then in tribes, subtribes, alliances and then genera.

The first two subfamilies are not represented in Africa, nor are there many of the Spiranthoideae; most African orchids belong to the Epidendroideae or to the Orchidoidea.

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. 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.

Subfamily Epidendroideae:

Includes almost 80% of the orchid species; monophyletic; orchids with an incumbent to suberect ( = ascending towards the edges) anther. This is the largest subfamily, 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

Subfamily Higher Epidendroideae:

Specialised clade within a more broadly defined 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.

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.

Bibliography and References:

Chase, M. W. 2005. Classification of Orchidaceae in the age of DNA data. Curtis's Bot. Mag. 22(1): 2-7.

Chase, M. W., Hanson, L., Albert, V. A., Whitten, W. M., and Williams, N. H. 2005. Life history evolution and genome size in subtribe Oncidiinae (Orchidaceae) Ann. Bot. 95(1): 191-199

CHASE, M. W., J. V. FREUDENSTEIN, AND K. M. CAMERON. 2001. DNA data and Orchidaceae systematics: A new phylogenetic classification.

Dressler, Robert L. 1981. The Orchids: Natural History and Classification. Harvard University Press 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.

History of the taxonomy of orchids

Mark W. Chase, Kenneth M.Cameron, Russell L. Barrett, John V. Freudenstein DNA data and Orchidaceae Systematics : A new Phylogenetic Classification by

Molecular phylogenetics and evolution of Orchidinae and selected Habenariinae

Orchid Tree: a phylogeny of epiphytes (mostly) on the Tree of Life

Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (1999). Genera Orchidacearum 1 - Apostasioideae and Cypripedioideae. Oxford Univ. Press.

Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (2003). Genera Orchidacearum 3 - Orchidoideae (Part 2), Vanilloideae. Oxford Univ. Press.

Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (2006). Genera Orchidacearum 4 - Epidendroideae (Part 1). Oxford Univ. Press.

Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. (2009). Genera Orchidacearum 5 - Epidendroideae (Part 2). Oxford Univ. Press.

Rasmussen, F.N.; Pridgeon, A.M., Cribb, P.J., & Chase, M.A. eds. (2001). Genera Orchidacearum 2 - Orchidoideae (Part 1). Oxford Univ. Press.