Distribution of species and genera

According to their distribution in the various continents , the orchid flora may be described as :-

1. Those of the Old World
2. those of the New World and
3. those found in both Old and New Worlds.

The Old World flora is characterized by such genera as Dendrobium , Cymbidium , Eulophia , Vanda , Phalaenopsis etc. and include all monopodial forms,i.e. , the whole tribe of Sarcanthine orchids. Genera like Cattleya , Laelia , Brassavola , Oncidium, Maxillaria , Zygopetalum, Sobralia , Epidendrum, etc. are endemic to the New World , whereas Habenaria , Orchis, Cephalanthera , Epipactis , Goodyera , Erythrodes,Spiranthes , Vanilla , Galeola, Pogonia ,Calanthe , Malaxis, Liparis etc., are found in both regions .

As Dillon (1971) has pointed out m this distinction into Old and New World species is more evident among the epiphytic forms than the terrestrial species . The latter , particularly those belonging to the primitive tribes fo Neottieae and Orchideae are found occurring in both the hemispheres . Among advanced forms , Calanthe, Malaxis , Liparis , Polystachya etc. with waxy pollinia are worldwide in distribution . The genus Bulbophyllum also corsses the Atlantic to occupy American territory . But apart from these few instances , epiphytic forms are sharply differentiated into Old and New World forms.

There are also genera which carry this differentiation a step further , being confined to particular regions of the continent , as Angraecums to Africa, Stauropsis to Malaysia , Neofinetia to Japan, Anguloa to Columbia and Calopogon to S.E. United States. The four genera of the Diandrous section occupy four different regions of the globe –Paphiopedilum in South East Asia and India , Cypripedium in the Northern temperate regions of Asia , Europe and America, Phargmipedium and Selenipedium in South Central America .