The bryophytes of the Water of Leith have been recorded by David Chamberlain and others over many years and this outing was mainly an opportunity to familiarise ourselves with some of the species previously found there. This section of the river has a large number of bryophyte species because Craiglockhart and Colinton Dells are wooded, humid, and base-rich. As the Water of Leith was once a source of waterpower for the many mills that lined its banks, some species are confined to the remains of these old stone structures and lades.
Our main interests were in the bryophytes on a wooded slope in Craiglockhart Dell, and those below a weir and along the associated lade in Colinton Dell, the two sites being in separate monads. Inevitably we were unable to resist looking at epiphytes on the branch of an oak tree which included two current and one former species of Orthotrichum, two Metzgeria species, Plenogemma phyllantha, and Cryphaea heteromalla.
A glacial erratic boulder marks the start of a narrow, steep path through the woods. On the slope above the path were Weissia sp., Plagiothecium succulentum, and lots of Cirriphyllum piliferum. We were able to compare the regular branching of the Cirriphyllum with the untidy, straggling mats of the abundant Brachythecium rutabulum. Much of the slope was covered by the bright green, fern-like fronds of Fissidens taxifolius, and a rotting log formerly covered in Campylopus introflexus now has only a small remnant patch of this invasive moss.
The recent dry spell allowed us the opportunity to explore the river just below a weir above Redhall Mill. On the exposed rocks were Orthotrichum rivulare and Porella cordaeana, and Liz Kungu found Cirriphyllum crassinervum and Zygodon stirtonii on man-made structures. Other species on exposed stonework were Hygrohypnum luridum and Hygroamblystegium tenax. This weir feeds an old mill lade and here we found further species, including Neckera complanata and two Schistidium species. As we left the mill lade we came upon another invasive species, Lophocolea semiteres, by the path near the lade. For those who had stayed to the end the outing finished with refreshments in the Water of Leith Centre.
David Adamson, February 2023Download a list of species recorded