Tortula muralis Hedw.   

Kingdom: Plantae
Phylum: Bryophyta
Class: Bryopsida – mosses
Order: Pottiales

British distribution: Common throughout Britain.
World distribution: Cosmopolitan.

A moss of rocks and walls, preferring lime-rich substrates, including mortar and concrete.

One of the most common urban species on walls, often the dominant moss on the wall face and able to grow on open brickwork which seems not to suit most other species.

The colonies have a typical cushion growth form, usually with numerous erect sporophytes (to 2 cm in height) and with distinctive hair-points ('excurrent veins') projecting from the rounded leaf tips.

Colonies also often have capsules at varying stages of maturity; the photograph below shows maturing capsules (already when photographed in early February) and also old capsules from the previous year. Production of sporophytes does not seem to be restricted to a single time of year in this species - a feature that may benefit it as a rapid colonist of open areas on rock surfaces.

The leaves show a number of adaptations to their exposed environment:

  • the projecting, "excurrent" veins, which together hold an insulating air layer over the cushion surface;
  • leaves twisting around the stem in dry conditions, holding capillary water between leaf and stem;
  • lef-margins recurved, giving mechanical strength;
  • upper leaf cells small and thick walled, to enable water retention;
  • outer surfaces of the upper cells strongly papillose, holding capillary water and allowing water transport over the surface.

Photographs: Paisley, Renfrewshire, various dates.

•   A.J.E. Smith (2004) The moss flora of Britain & Ireland, ed. 2, Cambridge University Press, Cambridge.

© A.J. Silverside
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