Plants of Mount Kinabalu (vol 2): Orchids; The

The orchids are considered by many botanists to constitute the largest family of flowering plants, with an estimated 15,000 to 30,000 species. Their only rival in size is the aster or daisy family, Asteraceae (Compositae), which may have about the same number of species. In spite of this great diversity, the Orchidaceae are not a family upon which human survival depends. Few orchids are used as food plants, none provides shelter, their medicinal sources may be only of psychological value and only one, the vanilla plant, has economic importance outside the enormous enthusiast and horticultural interest. Nevertheless, orchids have many other remarkable features that render them among the most fascinating of plant families. It is not possible to say that a particular group of plants is the most advanced, but the orchids surely represent one apex of flowering plant evolution. Not a single species is woody, generally considered to be a primitive feature. Orchids occur throughout the world from the hottest tropics to the arctic tundra, although they are far more abundant in the tropics. In pollination they have some of the most specialised mechanisms found in any plants, deceiving and even trapping insects that transfer their pollen. In most of them the pollen is united into compact bundles, the pollinia, a character that occurs in only one other completely unrelated family, the milkweeds (Asclepiadaceae). Many of them produce vast quantities of dust-like seeds, even numbering into the millions, in a single fruit. The seeds lack endosperm; a fungal symbiont is therefore required for germination. All species have a close relationship with mycorrhizal fungi, at least in their seedling stages, and depend on the fungi absorb nutrients. A high percentage of the orchid family, the most evolutionarily advanced, are epiphytes, using other plants for support although not obtaining nourishment directly from the host as would a parasite. A relatively limited number are saprophytes lacking chlorophyll. Two species in Australia even live and flower underground!