At this time of year the moss plants are lush and are growing well on mild, wet winter days, but in summer they can be baked by the sun during periods of drought that can last for weeks (if we're lucky!). This moss genus has a remarkable mechanism for resisting the long term effects of drought, thanks to specialised proteins called dehydrins and rehydrins within the leaf cells that protect the delicate cell membranes when the plants dry out and when they rehydrate again after rain.
This is a very droughted sample of a closely related species called Syntrichia ruralis subsp. ruraliformis (which used to be called Tortula ruraliformis before taxonomists changed their minds about its name). It grows in environments that are even more arid in summer than our garage roof - on coastal sand dunes. I subjected it to artificial drought - 10 days on a sunny indoor window ledge with no water.....
...... and here it is five minutes after one half of the cushion has been re-wetted, simulating rainfall ....
There are several plants commonly referred to as 'resurrection plants' (see Google for more) that have evolved the capability for this apparently miraculous recovery after drought and, understandably, the underlying physiological and biochemical mechanisms that allow them to tolerate drought are of great interest in scientists who are working towards breeding more drought-tolerant crops.
Some mosses are much tougher than they look. They were, after all, amongst the first plants to colonise the land surface around half a billion years ago..... and they are still here, after five major mass extinction events and drastic climate changes. Maximum respect for Syntrichia and related Tortula species, for sheer resilience and durability.
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