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Introduction Orchids can grow in a variety of habitats such as marshes and wetlands, on trees, in the ground, on cliffs, riverbanks and areas where decaying organic matter and the fungi that grow there provide food for orchids. Orchids can be divided into three main groups based on their habitat: terrestrials, epiphytes, and a subset of epiphytes called lithophytes. Orchids can also interchange their habitat depending on the circumstances in which they find themselves. For example, an epiphytic seed can land and grow in a well drained but still moist area, like a rock next to a stream, if there is enough moisture to sustain its growth. Terrestrial orchids These orchids have the ability to adapt to growing conditions that are quite varied: from boggy ravines to damp forest floors, from sandy dunes to semi-arid desert soil. The roots of terrestrial orchids sometimes produce tubers that lie just below the soil surface or even deep underground depending on the circumstances. Sometimes roots are sent directly into substrate such as soil. Temperate terrestrial orchids are often deciduous in that their flowers and leaves fade in winter and remain underground until the new growth season begins. New growth will then appear as a single leafy stem topped by flowers. Examples of terrestrial orchids include Cymbidium, Ladyslipper and Jewel orchids. Epiphytic orchids Epiphytic orchids grow on host trees. They are usually supported by the trunk or the thick lower branches of the host, though sometimes they perch on small twigs in the very top of the tree canopy. All epiphytes cling to their hosts with very strongly developed root systems. These roots take advantage of the moisture and organic debris that are caught in the crevices and bark of the host for nourishment purposes. All additional moisture and nutrients that are required are absorbed from the humid tropical air, rain, and mosses, ferns and fungal symbionts. Epiphytic orchids benefit from the microclimates offered by their hosts. Some epiphytic orchids evolved in shade or moderate dappled light and therefore favor growing on the trunk or lower branches of the host tree; others that require direct sunlight and ventilation will be found higher in the canopy at the top of the host tree. Some of the most notable and familiar types of orchids that are epiphytic are in the genera Dendrobium, Cattleya and Phalaenopsis. Lithophytic orchids Lithophytic orchids are mainly found in the tropical regions of the world. They grow on exposed rocks. They have strong roots that burrow into small crevices and absorb moisture and nutrients found amongst the moss and organic debris that collect in them. Some orchids such as the Hoffmannseggellas (Rupicolous Cattleyas of Brazil) grow amongst pebbles. The leaves of lithophytic orchids are often quite fleshy; they and the pseudobulbs (a part of the plant specifically modified for the storage of energy and derived from the part of the stem between two leaf nodes) carry the plant through any prolonged dry spells that might occur. Examples of lithophytic orchids include Dendrobium kingianum, Dendrobium speciosum, Bifrenaria and Maxillarias. Orchids: Where is my home? www.gardens.si.edu
