Orchids grow (nearly) everywhere. Only some desert countries (Mauritania, Kuwait, Western Sahara, Qatar, United Arab Emirates), some isolated, species poor islands (Ascension, St. Helena, Kerguelen, Tristan da Cunha etc.) and young coral atolls (Kiribati, Marshall Isl., Nauru) have no indigenous orchids. Desert regions are usually very poor in species, whereas orchids are remarkably tolerant to climate and reach into the far north (Greenland, Alaska) and in the subantarctic south (Tierra del Fuego, Macquarie Island). The number or species increases exponentially in the tropics and is extremely high in the mountainous tropics (Colombia, New Guinea, Indonesia, Ecuador, Costa Rica, etc.).
The highest numbers of species per region occur in Colombia, Ecuador, New Guinea, Brazil, Peru or Borneo. Large countries like China and India follow behind. In this statistics the Malesian islands are counted separately, however. Following political boundaries, Indonesia with over 5000 species would have by far the most species. The correct number for Indonesia can only be estimated, because a reasonable separation between Irian Jaya and Papua New Guinea in todays boundaries cannot be made.
It is quite surprising that the relatively small Ecuador turns out to be the country with the most orchid species (about 4000) This is probably an artificial result and caused by a comparably good treatment of Ecuador. Colombia most certainly harbours more orchid species than Ecuador and catches up quickly by better accessibility in the last years. If the whole island is treated, New Guinea would also be a runner-up for the most orchid species per area.
Tropical Africa is comparably poor in species, which is the same situation as for vascular plants and insects in total. Madagascar alone has nearly as many species as the whole tropical Africa. A most likely reason is the near-absence of a real tropical mountain flora in Africa. Many scientists assume that the tropical African rainforest did shrink several times to small islands, caused by major climate shifts.
If considering species density per area, the well known and highly diverse Costa Rica, still covered with many rainforests and cloud forests, shows up in first place, followed by Panama and Ecuador. Within the small islands, La Réunion with its cloud forests and an amazing 163 species tops the density (even if the new volumes of the Flore de la Mascareignes have reduced the numbers somewhat).
High endemism rates (of the species rich regions) are found on the isolated islands with an ancient flora (like Madagascar and New Caledonia), but also on tropical mountain islands like New Guinea, Brazil with a large surface area and the isolated atlantic forests, and, not surprisingly, Western Australia with an almost completely isolated floristic region.