Worcestershire Record No. 24 April 2008 p. 12

Dr Ann Hill

Tortula amplexa (Clay screw-moss) (Lesquereux) R.H. Zander, Syntrichia amplexa (Lesquereux) R.H. Zander, Barbula amplexa (Lesquereux)

The Worcestershire Bryophyte Group visited Wilden Marsh, a Worcestershire Wildlife Trust Reserve on 11 November 2007. During the day, Mark Lawley discovered the tiny acrocarp moss Tortula amplexa growing on the banks of the River Stour. This is a very exciting find for Worcestershire with only a few sites of the species known in the UK.

T. amplexa was originally discovered in the UK on recently disturbed clay at Moira quarry, Leicestershire and was seen there on at least five occasions between 1973 and 1988 (Porley and Hodgetts 1995). Subsequent visits to the same site in 1993 failed to find the moss: there had been substantial disturbance to the site. However, in 1994 a few small patches and a number of isolated shoots were re-discovered. In December 2006, whilst undertaking a bryophyte survey of a sand and gravel pit in Shropshire, Mark Lawley collected a puzzling acrocarp that was later determined as T. amplexa (Bosanquet, Godfrey, Lawley and Motley 2007). Prior to the 1973 discovery, the moss was only known from North America (Side and Whitehouse 1974). It was fortunate that Mark Lawley (who is one of very few British ,or European, bryologists to be familiar with the species in the field) was with us that day and found T. amplexa. However, the sample collected was too juvenile to have produced any tubers to allow positive determination. Therefore, in December 2007 a few of the group re-visited Wilden Marsh to obtain a better specimen of T. amplexa for determination. A fresh sample was discovered which was subsequently found to be identical to that which was found in Shropshire in 2006.

T. amplexa forms dense green tufts, reddish brown below, and up to 6 mm high. It has large leaf cells, recurved margins below and a nerve ending just below a rounded leaf apex (Smith 2004). The plant has abundant pale brown rhizoidal gemmae present. The main substrate for the species is soil (disturbed clay) and the normal habitat is extractive industry sites (Hill, Preston, Bosanquet and Roy 2007). However, with so little known on the species it may be that riverbanks are also a favourite habitat. The species is considered intolerant of even mild competition from other plants, so that it will apparently only grow in very disturbed habitats, such as riverbanks. The species is thought to spread by rhizoidal propagula through inadvertent human agency (Side and Whitehouse 1974). For more detail on the species please refer to the on-line British Bryological Society field-guide at http://www.britishbryologicalsociety.org.uk/ where there is an account of the species with excellent photographs.

The banks of the River Stour do fit well with T. amplexa having made its way out of disturbed clay pits and into the wider countryside. Has it spread down the River Stour as a result of the 2007 floods? The long term future for T. amplexa at Wilden Marsh is uncertain and it is doubtful whether there are any management options. As an introduction, perhaps the species is a curiosity that does not merit commitment of a large amount of resources and conservation? Is it an alien? The status and distribution of T. amplexa in Worcestershire (and in the UK) needs future research and survey and it would make an interesting bryological project to search for it up and downstream along the River Stour, and along other Midland rivers too, in order to assess how well distributed the species currently is.

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