Against the wall

Wall Screw-Moss (Tortula muralis)

While most of the garden goes into some level of hibernation for the winter, mosses are an exception. Right now, many of them are in their prime – lush and green and studded with numerous spore capsules. Our windowsills, roof tiles, and the top of the stone wall between ours and a neighbouring property are currently bristling with the lance-straight sporophytes of Wall Screw-Moss (Tortula muralis). This is one of the commonest mosses on brick and stone in Britain, and one of the first that neophytes like us learn to identify. Like the Grey-cushioned Grimmia (Grimmia pulvinata), this one has a long hair (called a "nerve") that extends from the tip of each leaf, as seen in the picture below. (Click on the picture to see it at a larger size.) Its leaves, when wet, like now, are bright green and opaque, developing into little cushions about a centimetre high. When it's dry, as in the summer, those nerves make the moss look frosty grey. Currently, the spore capsules end in spiky caps, but once the spores have finished developing, those caps will drop off. Then, a network of twisted hairs known as the peristome (the partial remnants of dead cells) which surround the mouth of the spore capsule will help to ensure that the spores are dispersed gradually rather than all at once. Given the vast number of little colonies sprinkled throughout the garden, this must be a pretty successful strategy.

Showing the twisted peristomes