Otmoor Stoneworts

Do you know what a stonewort is? Did you know that in addition to vascular plants (i.e. flowering plants, conifers and ferns) the Botanical Society of Britain and Ireland (BSBI) also collects records of stoneworts? I suspect that for some recorders the answer is 'no' to both. Stoneworts are a lovely, if obscure, group of aquatic green algae, but one could be forgiven for thinking they were some sort of weird vascular plant. Too big for proper phycologists, the BSBI seems to have adopted them out of sympathy.

I'd be really thrilled to receive any records of stoneworts from the county. If you feel like having a go then there's an excellent key to the commoner plants available from the BSBI here.

The Otmoor area has a lot of ditches and ponds, and it is not very difficult to find stoneworts round here. Indeed the moor is well known as an historic hot-spot for the nationally rare Tolypella intricata (tassel stonewort), recorded from the Saxon pond known as the Pill on Otmoor as well as a small number of ponds and ditches around the edge of the moor. The status of T. intricata is rather perilous nationally and around Otmoor owing to lack of pond and ditch management, and probably eutrophication, and it is listed as Endangered by the IUCN and is a species of principal importance (former UK BAP). The last report I know of it is from Nick Stewart, the national charophyte expert, who surveyed Otmoor for it in 2006 for the RSPB, finding a few plants in Greenaways on the reserve. I couldn't find it in 2016, but I was rather late — T. intricata gets going in March before aquatic vascular plants can grow up to out-compete it. The Freshwater Habitats Trust have been trying to rescue the plant, collecting soil (and, they hope, spores) from an historic Otmoor site for T. intricata and translocating it to ponds at the BBOWT reserve at Gallows Bridge Farm in the upper Ray, just within Bucks (V.C. 24).

Tolypella glomerata growing in a clean new ditch. The clusters of fertile branches give the species its name.

This weekend I thought I'd have a search for T. intricata in another Otmoor locality, Mansmoor in the parish of Charlton-on-Otmoor, to the north-west of Otmoor. Druce knew it from a ditch along Mansmoor Lane, which is now a dead end ending in the new railway. The area is anciently enclosed common land and most is a SSSI, including BBOWT's Wendlebury Meads, renowned for its ancient grassland. Sadly I didn't find T. intricata (the ditches were revolting), but I did find a stonewort almost as exciting: the nationally scarce T. glomerata. For some reason there are no records of this from Oxfordshire in the BSBI database or the NBN, but I know it has been recorded from the county, at least from Otmoor.

For this pretty little stonewort we have Chiltern Railways to be thankful, believe it or not. Although to build their new railway they had to clear many kilometers of hedgerow, an awful lot of new drainage has been constructed and many of these features now support stoneworts. My Tolypella was in a shallow surface water lagoon adjacent to the new bridleway over the railway from Mansmoor Lane, and which is now the main foot route to Wendlebury Meads. There were quite a number of plants scattered along the length of the lagoon. Where did the spores come from? Might T. intricata be in there somewhere too? You can be sure that I'll be looking for it.