In the section on distribution, some environmental conditions have already been mentioned. They are of the utmost importance to the plants; because they are the formative factors of life. From them, in a never-ending evolution, the plants were shaped and directed to their appearance. We do not suspect that it will continue to develop over long periods of time, only that there is such a thing, we know for sure from certain signs.
Which environmental conditions play a special role for the existence of the plant? The geographical latitude of the location is essential. It is under the influence of the position of the sun, so is an astronomical term. There are three zones between the equator and the pole: the heat, the temperate and the cold zone. The cold or polar zone is not taken into account.
1. The warm or tropical zone between the tropics has a high position of the sun, the differences in day lengths as well as between suns- and the shadow side are not very pronounced or not present, the temperature differences between the seasons are relatively small.
2. The temperate zone of the north- and the southern hemisphere between the tropic and the arctic circle has clearly pronounced temperature differences between the individual seasons and quite different day lengths. From this it can be seen, that light and temperature are primarily determinants of the climate, which in turn significantly shapes the environmental conditions. The term climate encompasses all of the factors light, Temperature and humidity, largely differentiated and influenced by atmospheric circulation.
The main distribution areas of tropical and subtropical orchids are as follows:
Asia: Ceylon and the Middle East, the high mountains (Himalayas) from Darjeeling to Assam and Burma, the Malay Peninsula with Indonesia, the Philippines, China and Japan.
Africa: Western tropical Africa, eastern tropical Africa, western extra-tropical and eastern extra-tropical Africa.
America: Central America, Westindien, tropical south america, andine tropical america. Within these areas the climatic conditions are of course very different. Details cannot be given here. What is essential is the uniformity of temperature and humidity in areas that are always humid, the fluctuations between day and night are within small limits. In contrast, periodically humid areas are significantly influenced by a dry season of more or less length. The orchids in this vegetation zone are equipped with particularly coarse leaves or shed them to overcome the dry period. The types of the always humid areas do not require such protective measures; they continue to grow almost without any noticeable interruption.