The first Sunday in June was hot and sunny but some heavy rain during the previous week made looking for mosses at Mount Caburn less hopeless than it might have seemed. It was too dusty and dry to look for roadside mosses, cows were crowding in all the shaded spots in the damp meadow near the river so I headed up the hill towards a south facing wood below the chalk pit. Blue butterflies, probably Common Blues, were flitting across the steep chalk grassland but I left the baking slope of Thyme and Marjoram (which will smell like pizza later in the summer) and headed into the trees.
It was warm in the wood and the ground was dry chalk scree but one moss was still partly hydrated after the recent rain. The Mediterranean moss Leptodon smithii is slow to expand when wet and slow to shrink again when dry. It likes to grow on base-rich bark and a huge old Ash tree was covered in dark green curls of aptly named Prince of Wales Feather-moss alongside drying, pale green curls of Homalothecium sericeum.
There were plenty more old Ash trees nearby with patches of Leptodon but none as extensive as this first patch. Dark circles of Frullania dilatata contrasted with the pale Ash bark and Zygodon viridissimus was common too. Radula complanata was new for the tetrad which already has 87 species recorded.
It wasn’t a huge surprise to find Leptodon here. Tom recorded it on numerous Ash trees on nearby Ranscome Lane as well as Weeks lane and Speaker’s Holt on the north slope of Mount Caburn. Last year I found quite a few patches on trees in a small copse just above the lane to the east of this wood and few weeks ago I found it growing abundantly if not particularly healthily on Hawthorn at the bottom of Beddingham Hill, visible from Caburn.
Small patches were visible on Hazel hedge in Moor Lane in March and last summer I found an isolated but vigorous colony on Ash near Piddinghoe.
Most of the 86 Sussex tetrads where Leptodon has been found are in wooded West Sussex and are on or near The Downs. There are a few small patches on Ash in the Devil’s Dyke area, (see the meeting report Summer Down Autumn sun), but I haven’t come across quite as many colonies as around the Glynde area.
Walking towards the old lime kiln near Fulking in much wetter conditions last September I stopped in a cow-trampled clearing to check the epiphytes on the surrounding trees. One horizontal Ash trunk over a particularly muddy slope seasoned with cow pats was coated in vivid green Leptodon smithii, bright and feathery after heavy rain.
I think this patch at the bottom of Perching Hill near Fulking is the largest I have seen. A nearby more vertical Ash tree had a small area along with abundant Neckera complanata. Radula complanata, Syntrichia papillosa and Cololejeunea minutissima were all present in small quantities. Other Ash trees around the clearing, even the really ancient ones were dominated by more common epiphytes.
Leptodon smithii was once common on Elm but I haven’t come across any on the Elm trees that survive in the Brighton area. It will also grow on Sycamore but nearly all the patches I have noticed are on Ash. It grows in areas with an annual average air temperature which exceeds 10 degrees C. Maybe it will spread further north with global warming but Ash dieback will not help its progress.