Classification of Orchid Genera 1
This is part one of a compilation of five instalments that first appeared in the Nambour Orchid Society newsletter between June and October 2021.
The Swedish botanist, Carl Linneaus proposed and developed a systematic method of classification of plants and animals between 1735 and 1759. His system was based on a structured division into kingdoms, phyla, classes, orders, families, genera and species. At the time, only eight genera were recognised in the Family Orchidaceae. By 1800, Olof Swartz had classified Orchidaceae into 25 genera. In the 1830s, John Lindley, regarded as the father of Orchid Taxonomy, recognised four Sub-families and described 1980 species. Through the 1850s, he progressively published his Folia Orchidaceae covering most of the orchid species known at the time. The basis of classification was floral and vegetative morphology with emphasis on the reproductive elements of the flowers as the primary determinant of genus and species. The Linnean System of classification continued over the next 150 years with many thousands of species being identified. Species names and, to a lesser extent, genus names changed from time to time as botanists/taxonomists refined the classification. Taxonomy was fertile ground for successive generations of botanists as they attempted to combine genera and/or species on the basis of similarities (lumpers) or divide them on the basis of differences (splitters).
In the 1950s, scientists developed techniques for the identification of deoxyribonucleic acid (DNA), a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms. For many years, access to DNA was not available to taxonomists at affordable cost. By the 1980s, however, scientists were amassing DNA data for a large number of orchid species and anomalies were becoming apparent in the historical classifications by genera, based on phylogenetic rather than morphological differences and similarities.
In the mid-1990s, a group of eminent scientists of the RBG Kew, led by Alec Pridgeon, Phillip Cribb and Mark Chase undertook the task of reassessing the classification of orchid species which now number around 24,000. They were joined by Finn Rasmussen of the University of Copenhagen in setting up the Genera Orchidacearum (GO) project. Over 200 scientists from many countries contributed to the project. In most instances, proposed changes were first published in peer-reviewed scientific journals before incorporation in GO. Contentious issues were referred to the Orchid Hybrid Registration Advisory Group (OHRAG) or its predecessor, the RHS Advisory Sub-committee on Orchid Hybrid Registration (ASCOHR) for resolution before publication. Membership of these bodies included eminent botanists from a number of countries but excluded the scientists working on GO. The results of this research were documented in the six volumes of Genera Orchidacearum totalling 2978 pages, published progressively between 1999 and 2014. The major changes were summarised in a paper entitled An updated classification of Orchidaceae by Chase et al. in The Botanical Journal of the Linnean Society, Vol 177, 2015. The new classification is summarised in an Appendix. I am authorised to make copies for training judges but I am not allowed to reproduce it in any publication. The article can be downloaded from https://academic.oup.com/botlinnean/article/177/2/151/2416341.
The Family Orchidaceae is divided into five very unequal sub-families. The larger sub-families are further subdivided into tribes and sub-tribes as listed below. The numbers of genera and species are quoted from the paper cited above and were current at the time of publication. Some more recently described species are not included. The five sub-families are:
Vanilla plantifolia
Apostasiodieae no tribes or sub-tribes, 2 genera and 14 species
Vanilloideae 2 tribes, no sub-tribes, 14 genera and 245 species
Cypripedioideae no tribes or sub-tribes, 5 genera and 169 species
Orchidoideae 4 tribes, 21 sub-tribes, 191 genera and 4631 species
Epidendroideae 15 tribes, 28 sub-tribes, 520 genera and 18730 species.
It can be seen that Epidendroidieae is by far the largest sub-family, containing 79% of all species. The sub-family Apostasiodeae is almost insignificant and is of little interest to hobby growers. In the sub-family Vanilloideae, only the genus Vanilla is of much interest, particularly the species Vanilla plantifolia which it is grown primarily as a source of Vanilla beans for food flavouring.
Paph. rothschildianum Phrag. besseae
The Sub-family Cypripedioideae contains all the “slipper” orchids. All genera have fused lateral sepals, leading to some botanists arguing that they should be placed in a separate family, but Kew has decided that they belong in Orchidaceae. Cypripediums are native to North America, Europe and Asia, generally growing in temperate to cold climates and rarely cultivated in Queensland.
At the time of publication of GO, there were 86 accepted species of Paphiopedilum, native to Asia and S.E. Asia, including New Guinea. They are popular in cultivation with almost 27,000 hybrids registered. Phragmipediums are native to Central and South America. The 26 accepted species are also popular in cultivation.
The Sub-family Orchidoideae
Most species in this family are described as terrestrial orchids because they grow in the ground or in decayed organic matter above ground. Many do not adapt to cultivation away from their natural environment and relatively few are cultivated by hobby growers.Tribe Codonorchideae contains only two species, both native to the southern region of South America.
Habenaria rhodocheila (photo by W. Harris)
Tribe Cranichideae contains eight sub-tribes, several of which are of interest to hobby growers. Sub-tribe Goodyerinae contains Goodyera, Ludisia, Macodes and Zeuxine. There are 211 species of Pterostylis in sub tribe Pterostylidinae. Spiranthes, with 34 species, is one of around 40 genera in sub-tribe Spiranthinae.
Tribe Diurideae contains 9 sub-tribes and many of the Australian native terrestrial orchids are in this tribe. Sub tribe Caladeniinae contains the genus Caladenia with 267 accepted species, more than half of them endemic to Western Australia. The sub-tribe Diuridinae contains Diuris (often called Donkey Orchids) with 70 out of 110 species endemic to Australia.
Tribe Orchideae contains four sub-tribes, two of which are of horticultural interest. Sub-tribe Disinae contains the genus Disa with 182 species, most of them native to Africa. The sub-tribe Orchidinae is large with 50 genera and 1749 species, the genus Habenaria accounting for almost half the latter number. Occurrence of Habenaria is widespread across all continents except Antarctica, including 17 species recorded in Australia and some are exhibited regularly. Habenaria rhodocheila pictured right is popular in cultivation. Ophrys, Orchis, Peristylis and Platanthera are other genera of interest in this sub-tribe.
Literature cited
Chase M. W., Cameron K. M., Freudenstein J. V., Pridgeon A. M., Salazar G., Van Den Berg C. and Schuiteman A., An updated classification of Orchidaceae, Botanical Journal of the Linnean Society, 177, 2015 151-174.
Pridgeon A. M., Cribb P. J., Chase M. W. and Rasmussen, F. N., Genera Orchidacearum, Vol 1 1999, Vol 2 2001, Vol 3 2003, Vol 4 2006, Vol 5 2010, Vol 6 2014, Oxford University Press.
Author: Charlie