After a wonderful vacation in Costa Rica (with ocean temperatures of ~85^oF) it was a shock to return to the Midwest and experience the Polar Vortex! Temperatures in West Lafayette, Indiana plummeted to a high of -2^oF and a low of -17^oF on January 30, 2019. Thankfully, temperatures rebounded to 56^oF yesterday (February 3, 2019) and it almost felt like spring! ![Temperatures.jpg](https://cdn.steemitimages.com/DQmeN5KMpbamRbNxgkKTDjZEECRygyF336qLXgwpmPYsPVM/Temperatures.jpg) Inspecting our magnificent 60-year old maple and ash trees yesterday, I was in awe at the rapid recovery of the epiphytes ([mosses](https://en.wikipedia.org/wiki/Moss) and [lichens](https://en.wikipedia.org/wiki/Lichen)) on their bark. Our ash tree is one of the few remaining in the area because of the [Emerald Ash Borer](https://en.wikipedia.org/wiki/Emerald_ash_borer); we have been treating the tree for the last several years to protect the tree from this invasive species. ![IMG_20190203_141920766.jpg](https://cdn.steemitimages.com/DQmc2A2xWea5qp3aDknkaiqfXCBhshNDszJdiJwyR2x2E9F/IMG_20190203_141920766.jpg) Epiphytic moss and lichens on our maple tree (February 3, 2019) ![IMG_20190203_141937265.jpg](https://cdn.steemitimages.com/DQmVCfkikJMBXEXVNYsWNQsegxGFU7yMUCxdnx9hxr9uLbR/IMG_20190203_141937265.jpg) Epiphytic moss and lichens on our maple tree (February 3, 2019) ![IMG_20190203_142004466.jpg](https://cdn.steemitimages.com/DQmWDZKgNF4Nen8DjVRZfriFFxQp7gocY8UkxMyya6hiKcu/IMG_20190203_142004466.jpg) Epiphytic moss at the base of our ash tree (February 3, 2019) Mosses and lichens are notoriously cold hardy and desiccation tolerant (Takezawa (2018), Tuba *et al*. (1996)). Their cold hardiness (freezing tolerance) is a function of their desiccation tolerance: by losing water this prevents intracellular ice formation (Lenné *et al*. (2010)). Upon rehydration they rapidly repair damaged membranes and their photosynthetic apparatus achieving full recovery in a few hours (Proctor *et al*. (2007)). This is facilitated by the production of proteins called rehydrins during the recovery from desiccation (Oliver *et al*. (2005)). Lichens are composite organisms that arise from a symbiotic association of algae and/or cyanobacteria with multiple fungal species. The algae and/or cyanobacteria provide photosynthate for the symbiotic fungus. The fungus helps gather moisture and nutrients from the environment, and produce protective antioxidants in copious quantities. They are estimated to occupy 6% of Earth's land surface and may be among the oldest living things (for further details, please see the Wikipedia article on [Lichen](https://en.wikipedia.org/wiki/Lichen)). **References:** [Lenné, T., Bryant, G., Hocart, C.H., Huang, C.X., Ball, M.C. Freeze avoidance: a dehydrating moss gathers no ice. Plant Cell Environ. 33: 1731-1741 (2010)](https://www.ncbi.nlm.nih.gov/pubmed/20525002) [Oliver, M.J., Velten, J., Mishler, B.D. Desiccation tolerance in bryophytes: a reflection of the primitive strategy for plant survival in dehydrating habitats? Integr. Comp. Biol. 45: 788-799 (2005)](https://www.ncbi.nlm.nih.gov/pubmed/21676830) [Proctor, M.C., Ligrone, R., Duckett, J.G. Desiccation tolerance in the moss *Polytrichum formosum*: physiological and fine-structural changes during desiccation and recovery. Ann. Bot. 99: 75-93 (2007)](https://www.ncbi.nlm.nih.gov/pubmed/17553826) [Takezawa, D. Mechanisms underlying freezing and desiccation tolerance in bryophytes. Adv. Exp. Med. Biol. 1081: 167-187 (2018)](https://www.ncbi.nlm.nih.gov/pubmed/30288710) [Tuba, Z., Csintalan, Z., Proctor. M.C.F. Photosynthetic responses of a moss, *Tortula ruralis*, ssp. *ruralis*, and the lichens *Cladonia convoluta* and *C. furcata* to water deficit and short periods of desiccation, and their ecophysiological significance: a baseline study at present-day CO₂ concentration. New Phytol. 133: 353-361 (1996)](https://www.ncbi.nlm.nih.gov/pubmed/29681071)

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