EPIPHYTES AND HEMIEPIPHYTES
Epiphytes are plants that root and perch on other plants or nonliving objects.
True epiphytes, also termed holoepiphytes, are plants that never root in soil; this type completes its entire life cycle anchored to a host plant, and receives mineral nutrients only from nonterrestrial sources.
A hemiepiphyte is strictly epiphytic for one stage of the life cycle but becomes rooted in the soil during another stage. A primary hemiepiphyte begins life as an epiphyte and later becomes rooted in soil, whereas a secondary hemiepiphyte begins life rooted in soil and later assumes an epiphytic life.
Some General Properties of Epiphytes and Hemiepiphytes
- Epiphytes and the epiphytic phase of a hemiepiphyte in most cases obtain water and minerals via adventitious roots that cling to or enter bark of the host plant or in the accumulated organic matter and litter at perch sites. These are also can have aerial roots. Aerial roots may adhere to the host tree or grow downward from the canopy, sometimes more than 30 meters to the shaded forest floor.
- Seedlings of secondary hemiepiphytes may have skototropic growth (seeks darkness, i.e., a tree trunk, as does a vine).
- Epiphytes live in habitats that may subject them to sharp environmental gradients and periods of high stress, and these have been important driving forces in evolutionary diversification.
- Many epiphytes occupy microhabitats that dry rapidly, and there has been strong selection for resisting drought. Most common is the occurrence of CAM, Crassulacean acid metabolism, a photosynthetic system that increases water-use efficiency and thus drought resistance. CAM epiphytes tend to be those with thick leaves or succulent green stems.
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