User:Risalu313/Poikilohydry

Poikilohydry is the lack of ability (structural or functional mechanism) to maintain and/or regulate water content to achieve homeostasis of cells and tissues. Poikilohydric plants can gain or lose water in their tissues in equilibrium with the environment. Frequently, it is coupled with the capacity to tolerate desiccation to low cell or tissue water content and to recover from it without physiological damage.

Description
There are several features that differentiate poikilohydrous plants from homoihydrous plants: 1. The ability to survive severe long-term desiccation,

2.   The capability to enter a state of anabiosis while dessicated,

3.   Heat and cold resistance while in an anabiotic state,

4.   Ability to quickly absorb water in the form of rain, vapor, or dew to achieve a hydrated state in equilibrium with the environment,

5.   Ability to turn on metabolic functions when water becomes available (and vice-versa),

6.   Capacity to go through many repeated cycles of desiccation and rehydration without cell damage, and

7.   Ability to perform photosynthesis at maximum capacity at low temperatures and light levels. Poikilohydrous plants can be separated into two groups; nonvascular plants such as the lichens and bryophytes that lack mechanisms such as a waterproofing cuticle or stomata, and vascular plants, such as ferns and lycophytes, which do possess cuticle and stomata. The vascular plants have largely lost the capacity to tolerate dehydration. Aside from most seeds and spores, only about 300 species of vascular plants are desiccation-tolerant, including resurrection plants such as Selaginella lepidophylla and many species in the genus Vellozia. Poikilohydry also occurs in many forms of algae, which may be able to survive desiccation between successive high tides, or during occasional stranding due to the drying of a lake or pond.

Ecology
Non-vascular poikilohydric plants occupy a range of diverse habitats depending on their growth form, size, and degree of desiccation tolerance. Bryophytes and lichens readily colonize the surfaces of trees, rocks, and other substrates in all but the most arid climates from the equator to the poles. They are most common in areas that are intermittently dry with periodic and predictable wet seasons. Poikilohydric vascular plants can be found in some deserts, and many species exist on inselbergs in Brazil, Africa, and Madagascar.