I was walking in Priory Wood and noticed mosses hugging the trunks at the bottom of each young tree. Going on hands and knees to look closer I felt I was entering a miniature rainforest, of minutely divided fronds and dripping with moisture.
As a child I used to love visiting old houses or castle, with the sense they gave me of being in touch with history. Looking at the mosses in Priory Wood sends shivers down my spine as I realise I am looking at one of the very earliest plant forms to develop and so am seeing survivors from early evolutionary history, taking me back, as it were, millions of years.
As the most primitive of land plants mosses have no roots, no flowers or fruits. They have no vessels (or vascular system) to carry fluid around their structure. Yet they are so well adapted they are immensely successful, occurring across the world and have approximately 22,000 different species. As I continued my walk I started to look out for mosses and I realised how many moss species can be seen growing on the tops of walls – and you can get a great view of them without getting damp knees from kneeling on wet ground! I suddenly aware how alive the church wall around St Mary’s is.
As I started writing this post, I looked out of my window and realised moss was right in front of my eyes – all over our garage roof. The moss on the roof is tightly compact in a form known as ‘cushions’. As mosses have no roots and no vascular system they are dependent on the moisture in the air. Where they are exposed, as on our garage roof, they need to stay tight and compact, in ‘cushions’, to reduce evaporation from their cells. Staying low down they are growing on what is called ‘the boundary edge’ between the ground and air. We know when we are in a windy place and lie down, it is much less blowy close to the ground. Mosses in exposed places lie low to keep out of the drying wind.
However, a problem comes when mosses want to reproduce. Mosses have no seeds, but produce spores. These need to find a suitable new patch of bare ground on which to grow. They need to fly! Yet the moss is growing low down out of the wind. The solution: the moss grows stems from which to launch their spores into the more turbulent air above. The length of the stem depends on how out of reach that turbulent air is. In a forest the stems will be longer than those from moss growing on our exposed roof.
Mosses play a vital part in our ecosystem. Their leaves have to be wet for the exchange of oxygen and carbon dioxide and so photosynthesis to be possible. They are therefore adapted to soak up and retain moisture for as long as possible. Their dampness creates a micro climate of humid air which benefits other plants and creatures that live in their vicinity. Mosses are also an indicator of air pollution. Their leaves are only a single cell thick and they don’t have the protective cuticles that so-called ‘higher’, more evolved, plants have. When sulphur dioxide or nitrous dioxide from car exhausts mixes with this water it turns to acid killing the leaves and so the plants.
Mosses have adapted to survive periods of drought. To demonstrate this, collect some moss fronds and gently dry them out, for example in the airing cupboard. Then put them on a plate with drops of water underneath. You will be able to watch the fronds revive, with renewed colour and shape.
I recently read Robin Wall Kimmerer’s book ‘Gathering moss: a natural and cultural history of mosses’ which has introduced me to the extraordinary world of mosses and much of the above comes from what I have learned from her book which is a beautiful description of her lifelong study and awe of mosses.
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