Classification of Orchids

Every system of classification should reflect a natural order, but in the case of orchids, the situation is unbelievably complicated.
So, How is it possible, by observing and studying the 25000 (yes you read well, 25 thousand) species of orchids that exist worldwide, to form any idea as to how they have evolved and become differentiated in the course of time?
What criteria can be used to group them in such a way as to take into account their potential genetic affinities?
Little wonder that botanists have come up against such a wealth of complex problems in their attempts to formulate a coherent classification.
The task of the taxonomists, the specialists in classification, is all the more difficult because there are extremely few orchid fossils, since for various reasons these plants are highly unsuited to fossil formation. The existence of such fossils would, needles to say, have been invaluable for establishing a so called natural classification, based on archaic forms that an understanding of the genetic affinities of modern forms, Unfortunately, the most ancient orchid fossil dates back no more than 12 million years, all too little in relation to present day notions as to the origins of the species, but too much in the context of ideas prevailing 20-30 years ago.
Orchids in fact, are plants which are still in an active phase of evolution, as indicated by a multitude of species, that are often capable of being hybridized. This might suggest that it is an extremely young family which appeared on  Earth only about 2 million years ago.
This, presents a paradox that must lead us to reconsider many of our conceptions relating to the organization of living things.
In fact, orchids are a very ancient and at the same time, evolutive family. As a result, it is the most diversified of all families of flowering plants.
After a good deal of trial and error, it ow transpires that the most reliable cirteria, for example which best reveal the relationship between species and genera, are the structural features of the sexual organs (anthers and pollinia) and hence, in the case of orchids, the structure of the column, the pollinia, the viscidium and the stigma. Linnaeus, in the early 1800's deserves credit for having underlined the merit of this method of classification.
More recently, the examination of embryonic forms has emerged as an excellent taxonomic criterion (Yvonne Veyret), in accord with the ideas of other authors who have based their classification on macroscopic criteria.
However, one of the most decisive criteria is still the study of chromosomes, particularly their numbers.

Many others criteria may also be utilized as a possible reference for classification, such as the form, function or structure of this or that vegetative or floral organ. But their value is, in most cases, merely complementary. It has often happened, indeed, that the same characteristic will have appeared at different moments in the evolution of different subfamilies or distinct tribes.
This seems to be the case of epihytism but also of numerous other features.
Although, to some, orchid classification may seem a fruitless exercise, the purely intellectual pursuit of grouping plants with common origins and characteristics is in itself rewarding, while for growers the value is immense.  Close relationship points to the existence of close inherited genetic traits and thus important possibilities for hybridization. Moreover, although there are many exceptions, close relationship of them implies common cultural needs.




Dressler's Classification:


Among the principal authoritites in the classifcation fo orchids over the years are John Lindley (1860), Rudolf Schlechter (1926), Robert Dressler (1974) and Peter Hunt (1978). Although all classifications proposed to this day remain the subject of debate and controversy, the one referred to most frequently is that of Robert Dressler.
His method of classification distinguises the following categories of groups or subsidediary groups (taxons):

• Subfamilies (total of 6)
• Tribes
• Subtribes
• Genera
• Species
• Varieties

Much controversy has surrounded this classification and different authors have challenged it on particular points:

• Should one subfamily or part of the subfamily be included in another? Or should 2 subfamilies be grouped to make a third one? (thus, Garay's classification takes a part of the Orchidoideae, a part of the Epidendroideae and the Spiranthoideae to make up the single subfamily Nettioideae
• Should 2 or 3 closely related genera be combined in a single one? (as it happens with Bulbophyllum and Cirrhopetallum)
• Should a variety become a distinct species?
• Should a genus be broken up?

These dscussions are often superficial, not to say irritatin, because they sometimes give impression that, in nature, such precise limitationds and catergories do not exist. But they do have the merit, in many instances, of furthering knowledge of orchids whilst enabling botanists themselves to establish their own rudiments of classification according to their personal preconceived ideas; broadly speaking, they go for lumping or splitting.

It is now generally believed that the orchids became differentiated about 120 million years ago, deriving from the ancestral order Liliales. Of these the Cypripedioideae and above all, the Apostasioideae (an archaic form of orchid) whould seem to be closely related, at least with regard of the structure of the column (2 fertile staments in the Cypripedioideae and 3 in the Apostaisioideae).
According to Dressler, there are 4 subfamilies of orchids characterized by the presence of one fertile stamen, with pollen clustered in masses of pollinia; the structure of the pollinia and of the column distinguishes between these subfamilies:

• Orchidoideae: One anther joined to the column, pollinia divided into packets and linked to a viscidium. These plants are almost exclusively terrestrial.
• Spiranthoideae: The stamen is affixed to the rear of the column; the pollinia are soft and friable; the viscidium is anterior. These plants are also almost always terrestrial.
• Epidendroideae: the stamen is protected by an easily lifted operculum; the pollinia are waxy in texture, with an adherent part but no viscidiu. These plants are either epiphytic or terrestrial.
• Vandoideae: the stamens are protected by an operculum, the pollinia are attached to one or two hard viscidia. These plants are almost exclusively epiphytes.

By taking into account many other features of both, the plant and flower apparatus, the 4 subfamilies are divided into 21 tribes:

• Subfamily Spiranthoideae: 

Subfamily Epidendroideae:

1. tribe Erythrodeae
2. tribe Cranichideae

• Subfamily Orchidoideae:

1. tribe Neottieae
2. tribe Diurideae
3. tribe Orchideae
4. tribe Diseae

• Anomalous tribes

1. tribe Triphoreae
2. tribe Wullschlaegeliae

• Subfamily Epidendroideae:

1. tribe Vanilleae
2. tribe Gastrodieae

• Tribe Epipogiaeae

1. tribe Arethuseae
2. tribe Coelogyneae
3. tribe Malaxideae
4. tribe Cryptarrheneae
5. tribe Calypsoeae
6. tribe Epidendreae

• Subfamily Vandoideae:

1. tribe Polystachyeae
2. tribe Vandeae
3. tribe Maxillarieae
4. tribe Cymbidieae

Enough for today right? too much information in only one post...

Thanks to Gerald Leroy-Terquem & Jean Parisot for this wonderful learning material.