The Squirrel Trail – In Search of Bryophytes

It’s Sunday 25th March, the clocks have gone forward which means officially summer time is here although most of us would be satisfied with more positive signs of spring rather than a forecast of snow in places. Sunday, however, was a spring-like day with sunshine just right for a stroll round Castle Eden Dene looking at mosses and liverworts. Castle Eden Dene is the largest area of semi-natural woodland in north-east England and is known for its yew trees, ancient oak and ash. It is a National nature Reserve, managed by Natural England and has some spectacular ravines and evidence of land slippage– Click Here for a brochure.

Castle Eden Dene slippage


Succession on mosses on aggregate rock near Castle Eden Burn

The Dene is a result of post glacial melt waters which carved out some spectacular limestone cliffs and gorges. The Castle Eden Burn flows at the bottom of the gorge but often disappears in the summer. At the bottom of the Dene the area remains damp and moist and is therefore a particularly suitable environment for mosses and liverworts to thrive. On our walk round today in many places it was actually quite dry but we all saw how a little bit of water soon revives a moss.

So, what is this moss?


Eleven keen botanists set off with instructions not to stop looking at every moss seen but to gather round at a particular spot so we could all get to grips with the structure of a moss. This was a useful way for beginners because none of us got overloaded and confused with the Latin names and the terminology. At this stopping point we discussed the difference between an Acrocarp moss and Pleurocarp moss. Mosses are divided into two large groups; Acropcarps – recognised as having capsules at the tip of their branches. They grow erect, are simple or sparsely forked, unbranched and often in tufts or cushions. This was illustrated by Grimmia pulvinata (grey-cushioned grimmia). The tip grows into a long grey hair point which is almost as long as a blade. To see this clearly and all other mosses it is essential you use a good lens the strength of which suits your eye sight.

Grimmia pulvinata (grey cushioned grimmia) – acrocarp moss showing capsules

Pleurocarps have capsules coming off a side branch. They are usually freely branched and grow into interwoven mats. They usually have curved capsules. Capsules are an important identifying feature. It is also important to establish whether or not there is a nerve and if the moss is a branching type whether it is Bi-pinnate or Tri-pinnate.

Thuidium tamariscinum (tamarisk moss) showing tripinnate branches pleurocarp


Brachythecium rutabulum (rough stalked feather moss) showing capsules on side branches – pleurocarp


Some of my personal favourites were Mnium hornum (swan’s neck thyme-moss) identified by its capsules in the shape of a swan’s neck. Also Fissidens taxifolius (common pocket-moss). This a neat moss rather like a fern with a nerve that runs to the tip of the leaf. Its capsules are plentiful. Thuidium tamariscinum which is a bright yellowish green and one of the most distinctive of the pleurocarps. These are tri-pinnate and form loose mats.

Mnium hornum (swan’s neck thyme-moss) with capsules at top of picture – acrocarp


Fissidens taxifolius (common pocket moss) – acrocarp

We did look at a few liverworts including the Pellia epiphylla, (overleaf pellia). The first liverworts arose from green alga some 400,000,000 years ago. They are divided into two groups, thallose and leafy liverworts. They reproduce by shedding spores. There are about 8000 different species including 25 that grow in Antarctica.

Pellia epiphylla (overleaf pellia) with black spore capsules – thalloid liverwort

It was hard of course not to look for other plants, trees, ferns and listen to bird song but most of us kept to the subject. We did see the first  Primula vulgaris (primrose), Petasites fragans (winter heliotrope), Anemone nemorosa (wood anemone) amongst several others which we would have identified if we were conducting a survey. Click here for a list of species identified on the day.

I should like to thank Gaynor and Bill on behalf of everyone for a thoroughly enjoyable stroll looking at the mosses and liverworts. We were all helped by the thorough preparation and paperwork given to us. I am sure Gaynor’s enthusiasm rubbed off on everyone including those who weren’t absolute beginners. For those who didn’t get a chance to write it down the book Gaynor was using was, “Field Guide to Mosses and Liverworts of Great Britain and Ireland”. See

Thank you also to Keith for recording and Lesley for photography.

Carole Lloyd

If you are interested in wild plants, of any type, the Durham Wildlife Trust botany group has a comprehensive programme of events over the coming months. There is a wide range of experience and expertise amongst the group and all are welcome to join in. For more details email or see the DWT website.