Poikilohydry

Poikilohydry occurs in such organisms as lichens and bryophytes, which lack mechanisms such as waterproofing cuticles or stomata that can help resist desiccation.

Frequently, poikilohydry is coupled with the capacity to tolerate dehydration or low water content of cell tissue and to recover from it without physiological damage.

2011, T. G. Allan Green, Leopoldo G. Sancho, Ana Pintado, Chapter 6: Ecobiology of Desiccation/Rehydration Cycles in Mosses and Lichens, Ulrich Lüttge, Erwin Beck, Dorothea Bartels (editors), Plant Desiccation Tolerance, Springer, Ecological Studies 215, page 113, The strategy of poikilohydry was almost certainly primitive and evolved from the production of desiccation-tolerant spores (Oliver et al. 2000). Organisms employing poikilohydry are confined to a small overall size, in particular because of the limitations to water transport that relies on capillarity (Proctor and Tuba 2002).

Nonvascular cryptogams, particularly the lichens and mosses, form a majority of the species and biomass exhibiting poikilohydry within desert regions of the world, including North America.

Their small size and ability to adhere to solid substrates allows mosses to occupy habitats where poikilohydry provides a unique advantage, but these characteristics set limits on their distribution to specific types of environments where tracheophytes are unable to dominate.