Glorious Reservoir Mud

After the long dry summer reservoir levels are low and wet autumn weather is only just beginning to noticeably raise water levels but has wetted the bare margins of the draw down zone making an excellent year for mosses of this habitat.

Ardingly reservoir was created in 1978 when Shell Brook, a tributary of the River Ouse was dammed. It feels settled into the landscape of ancient woodland and sandstone rocks but fabulous rocky habitats must have been lost as we have old records for a long list of rarities of sandstone from below Balcombe mill. There are a few boulders now but they are scattered and nowhere near as rich, although more might be hidden on private Balcombe Estate.

A couple of weeks ago the water was incredibly low but as there was such a carpet of bryophytes at the top of the muddy margins I didn’t need to venture to the waters edge.

The most noticeable mosses were Tortula truncata and a moss that looked a bit like Aphanorrhegma patens but smaller with some almost black capsules, lax leaves, immersed capsules on the mystery moss and clear of the leaves on Tortula truncata.

Physcomitidrium readeri

When I checked it microscopically at home I was foxed. The leaves were barely toothed with a faint nerve. The capsule was round with a short, pointed beak and the spores were large, about 30 microns, and spinulose. It didn’t match anything in Smith so I browsed Michael Lüth’s fabulous Mosses of Europe: A Photographic Flora, and came across photos of Physcomitridium readeri taken by Tom Blockeel in 2018 at Ladybower reservoir in the Peak District. So I sent some to Tom B. who confirmed it. When he discovered it at Ladybower it was a new species for Europe and now there are just four records in Britain. It’s new to Sussex and the south-east so quite an exciting find!

A Weissia with capsules emerging on a shortish seta looks as if it will be Weissia rostellata but I would like to check it in a few weeks time when it will have matured a bit. Dicranella staphylina and Pohlia melanodon were more familiar mosses but an Ephemerum looked like a new species for me.

The leaves were long and spreading, lacking the jagged teeth of many Ephemerum sp. and with a distinct nerve. The colonies showed up as a dark green on the mud which seemed to be a protonemal mat under dull leaves and capsules. Ephemerum sessile has now been found in 16 tetrads in Sussex on pond and reservoir edges and damp woodland rides.

I didn’t find the Bryum klinggraeffii or Pseudephemerum nitidum that David Holyoak found here in 2001 but there are still miles of unexplored reservoir edge, no doubt rapidly disappearing under water after this weekends deluge of heavy rain.