Cytology and Phylogeny

Today ‘ Orchidology’ has become a very important branch of science. The various aspects of the process of hybridization, propagation, culture , the various physiological requirements of orchids for the maximum output of flowers , the pests and diseases which they have to reckon with and the corresponding preventive measures etc., have been studied with a good deal of thoroughness. But those purely botanical fields which have no immediate bearing in the applied part of the science have suffered a great deal of neglect . Unlike other plant families, cytology has very little to do with breeding program in orchids . Related species and genera interbreed , irrespective of chromosome size and number and the problems posed by the consequent sterility , if at all there are any , are now being effectively dealt with by various methods of vegetative propagation and clonally multiplication. So much so a knowledge of orchid cytology is not very necessary to the average orchid breeder , and investigation in this field are mostly left to the scientist who deals with it purely for the sake of knowledge. Stern (1960) once remarked that there are far too many orchids in relation to the people studying them. In no other context is this more true than in the case of orchid cytology. Considering the vast number of species in the family , it is to be admitted that our knowledge of its cytological aspects is , indeed , very poor. Till recently , few attempts have been made to clarify the cytological situation in orchids and very little intereset was evinced in it . This was especially true with the tropical species , while the mother temperate forms received a little more attention .

It is true that determination of chromosome numbers in orchids stated as early as the nineteen- twenties ( Fuchs and Zeigenpeck, 1924; suiguira, 1928; Hoffmann , 1929 etc.)but it progressed at a very slow pace. In 1960, after nearly 35 years of orchid cytology , only 370 species in 84 genera were investigated , in a family which at that time , had more than 12,000 valid species . Even this meagre knowledge could not be claimed as a representative sample of all the tribes . The orchid cytologists of earlier days concentrated mostly on genera of horticultural importance like Paphiopedilum, Cattleya and its allies , Dendrobium, Cymbidium , Odontoglossum , Oncidium, Vanda and Phalaenopsis . More than 200 of the chromosome counts were of species belonging to the above genera . Meanwhile , there were several groups like the Australian representatives of Neottieae which were totally neglected . The largest of all genera of orchids, Bulbophyllum , with nearly 2000 species and a very wide distribution in the Asiatic and African continents , had only a single species investigated .

What little was done to study the cytology of orchids in genera; and in groups , in these early days , is indeed worth mentioning . Pioneer among those were the works of Hoffmann (1929, 1930) on orchids of the north temperate regions , of Humphrey (1932, 1933) on certain species of Habenaria , of Miduno (1938, 1939, 1940 a &b) on a few Japanese orchids and the very valuable studies on British marsh orchids by Heusser (1938), Hagerup (1938), Vernuelen (1938, 1947) and Heslop-Harrison (1948, 1951). It was in the nineteen-sixties that large scale attempts were made to explore the field of orchid cytology. The chromosome numbers and mutual affinities of the Sarcanthine group of orchids have been clarified to a great extent by the Hawaii team of orchidologists (Woodard , 1951; Tanaka & Kamemoto 1961; Shindo and Kamemoto, 1962; Tara and Kamemoto , 1970 ,etc.) Studies of Blumenschein (1960) , of Chardard (1963) on 107 species of orchids, of Tanaka (1965) on 111 species of Japanese orchids, of Jones on Dendrobium (1963) Polystachya (1966) and the tribe Vandeae Lindl. (1967) and those of ar-Rushdi (1971) on several African species , have added considerably to our knowledge of the wild species of orchids. Meanwhile , Indian orchids have also received their share of attention ( Mehra and Pal, 1960; Sharma and Chatterji , 1960 , 1961-1966; Mehra and Bawa , 1962; Chatterji, 1965, 1968; Chennaveeriah and Jorapur , 1966; Mehra and Vij, 1971; Vij and Vohra , 1971; Mehara and Vij, 1972, etc.). These reports are mainly on species from Northern and Eastern India . Chromosome numbers of 87 species of orchids , 51 of which were native to Southern India , and their inter-relationships were also studied in the Department of Botany, University of Kerala by one of us (Vatsala , 1964, Ph.D .thesis).