Connor Fitzpatrick is responsible for today's write-up:

This bryophyte (liverworts, hornworts and mosses), belongs to the class Bryopsida. Also referred to as the joint-toothed mosses, the Bryopsida account for 95% of all moss species. The common name refers to the fact that the peristome teeth found on the sporangium of these mosses are made from fragments of whole cells. The peristome teeth of this moss are hidden underneath a calyptra and an operculum. The UBC Biology 321 course website does an excellent job explaining moss morphology.

This particular moss, Tortula muralis, has a wide distribution and can be found on all but one continent. This incredible range is due in part to an ability to tolerate desiccation (water loss). Eric in SF@Flickr noted that he found this moss growing on a brick wall. As Daniel mentioned in a previous BPotD posting, ectohydric mosses such as Tortula muralis rely on external water conduction. Mosses are in constant equilibrium with their habitat. Water is travelling in and out of cells depending on the available moisture in the environment, a condition known as poikilohydry. Several physical features help this moss retain water in low-moisture environments (such as brick walls), including leaf extensions (awns) which reflect light & increase the laminar boundary layer and very dense, short growth. Another bryid moss that can be found on similar substrates and shares these features with Tortula muralis is Grimmia pulvinata. The ability to resist desiccation at the cellular level is an active area of research. Oliver et al. (PDF), compares the mechanisms of desiccation tolerance in bryophytes to those of vascular plants with the hopes of coming to a better understanding of the evolution of this ability throughout land plants. One such mechanism (PDF) found in the moss Tortula ruralis (not a typo), is the conservation of polyribosomes during desiccation. Polyribosomes are needed for the translation of mRNA into proteins. Upon rehydration, these conserved polyribosomes allow the moss to resume protein synthesis.

An understanding of the processes employed by mosses and vascular plants to “cope with severe water deficits has economic and agricultural implications that directly relate to crop productivity in an ever challenging and changing environment” (via Oliver et al.). Thank you to Eric in SF for a very interesting photograph (original via BPotD Flickr group pool).