One of the largest families of flowering plants, the orchids (Orchidaceae), are also one of the most highly diverse and specialized families. Orchids range in size from a few millimeters to over 13.5 meters tall. Orchids grow in habitats ranging from some of the coldest and wettest parts of the earth to the hottest and driest parts, from the polar regions to the equator. Being so diverse and prevalent, the orchids have evolved many extremely specialized ways of pollination. Many of the orchids produce flowers which resemble female insects in order to attract unsuspecting males. When the male insect attempts to mate with the flower, pollen is attached to its body, which will then be transferred to another flower that the male insect mistakes for a female. The orchids are in fact so specialized that many of them are only pollinated by a single specific insects.
Since many orchids are epiphytes they have also evolved specialized roots. These roots attach to trees or other objects and fasten the plant in place. The roots are covered with a spongy layer of tissue known as velamen that has the ability to become almost transparent when wet, which allows the inner root to carry out photosynthesis. In periods of drought, however, the velamen becomes hard and protects the plant from dehydration.
Along with their reliance on specific insects, orchids also rely heavily on fungi. The seeds of orchids are extremely small and do not have the starch storage tissue, known as endosperm, that most other plant seeds do. This means that they have no nutrients to germinate and must find a suitable fungus. The fungus actually provides the energy for the orchid to germinate and this relationship usually continues for the life of the orchid.