Distributional frequency

As in any other orchid population anywhere else in the world , here also there are species which find conditions existing in South India conducive for growth and reproduction , as well as species which just manage to survive in a few localities . Most of the hardy species occur in the plains and these are the most prolific of the lot,eg., Acampe wightiana, Dendrobium macrostachyum, Pholidota pallida etc. Among species which thrive on hilly ranges at low elevations , Aerides ringens , Rhynchostylis retusa , Polystachya flavescens etc., are the commonest . In the rain-shadow areas , Vanda tessellate and Vanda testacea are the most common species .

Variations in morphological aspects of the same species existing in different localities and different altitudes are great . An interesting example is provided by Aerides ringens which occurs with slight variations from 300 m above sea leavel to 2000 m . At 300-600m this plant usually has thick dark green leaves heavily mottled with purple and profusely branched panicles with white flowers having the faintest touch of pink . At elevations of 800-1200 m the plants have paler and wider leaves. The main axis of the inflorescence grows horizontally from which upright branches are given off . Flowers are larger and fewer in number and pink in colour . Higher up between 1300 – 1700 m the leaves are again dark green and mottled with purple , but inflorescences are seldom branched and flowers are a bright magenta in colour .

Among terrestrial orchids , Calanthe masuca , Geodorum densiflorum , Eulophia macrostachya , Acanthephippium bicolor etc., are the most widely distributed . In the higher altitudes Dendrobium herbaceum , Eria polystachya , Eria pauciflora are the most abundantly and widely distributed species. Species like Dendrobium heterocarpum ,D. nutans ,D. heyneanum , Trias stocksii etc., are widely distributed but few in number in each locality , whereas Bulbophyllum aureum , Phalaenopsis decumbens , Thrixspermum arachnites , Rhynchostylis latifolia , Phaius luridus were indeed scarce occurring in one or two localities .