Blysmus compressus

Taxonomy 

Blysmus compressus (L.) Panz. ex Link. Flat-sedge.

Synonyms include:

  • Scirpus caricis Retz
  • Scirpus compressus
  • Schoenus compressus

Chromosome No.: 2n = 44, 78 (Stace 2010).

Blysmus compressus

Photograph: C. O'Reilly

Identification 

Readily distinguished by its compact terminal inflorescence with distichously arranged spikelets.

Blysmus compressus

Photograph: C. O'Reilly

Status 

A ‘vulnerable’ Red Data Book species and hence added to the list of UK Biodiversity Action Plan priority species in 2007; not previously listed as threatened despite being very rare in Wales, Scotland and many counties in Southern England. It has suffered a severe decline, being lost from more than half its pre-1930 hectads by 1962 and 40% of its post-1930 hectads since then. The main causes appear to be grassland drainage and improvement as well as eutrophication and the cessation of grazing. Now extinct in many English counties (e.g. Kent; Leicestershire, Nottinghamshire, Middlesex, Shropshire, Staffordshire, South Devon, Surrey and West Suffolk). Similar declines have been reported elsewhere in Europe (e.g. Croatia and Finland).

Distribution 

Throughout the temperate zone of Europe as far north as southern Scandinavia. In Britain it is a widespread but localised species. It has been recorded in the majority of English counties but only in abundance in the north and west, where it is confined to the margins of rivers and streams, flushes and springs on base-rich rocks. It is very rare in lowland England, although there are still large populations along the Rivers Kennet and Thames. Confined to Brecon in Wales and in Scotland there are no populations north of the Central Belt. It does not occur in Ireland. Lowland; ascending to 490 m in County Durham.

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Ecology 

A rhizomatous perennial of open, sedge-rich areas in calcareous flushes, marshes, fens and damp grassland (sometimes slightly saline as at Marcham in Berkshire) and pond and stream borders subject to flooding. It also occurs in brackish ditches at the head of saltmarshes (Halliday 1997), dune slacks where it appears to share the same niche as Juncus balticus (Smith 1984) and alluvial ‘meadows’ that have developed on stabilized shingle (Graham 1988). On chalk downland it is confined to spring-lines, and coastal populations occur in dune slacks presumably enriched by shell-sand. It appears to favour transitional habitats (Westhoff & van Leeuwan 1962), and almost always occurs where there is some movement of base-rich groundwater even in acid Sphagnum bogs where springs ensure a constant supply of base-richness (e.g. chalybeate springs in the New Forest; Brewis et al. 1996). In v.c. 80 and 81 Blysmus compressus has most of its colonies in a very distinct burnside habitat – a shelf below normal bank level burn occupied by short grass turf. On the North Tyne it also occupies the extreme riverside edge niche in inundated habitats such as rocky spits or islets growing with species such as Trollius europaeus. It is much rarer in the more strongly flushed areas, as the vegetation is much too tall for it. On moorland it can occupy flushes as the associates do not compete so strongly with it. It is not mentioned in the NVC although Graham (1988) records it from Carex dioica-Pinguicula vulgaris mires (M10) in County Durham. This is probably the typical community in Northern England where it grows with rarities such as Bartsia alpina and Juncus alpinoarticulatus. In southern and eastern England it occurs in species-rich fen meadows including MG8 Cynosurus cristatus-Caltha palustris grassland and M23 Juncus effusus/acutiflorus-Galium palustre mire. Grazing is important in keeping these habitats open although both over- and under-grazing are likely to be detrimental in the longer term. The flowers are hermaphrodite and wind-pollinated with fruiting continuing until September. Little is known about its seed or reproductive biology.

Further Work 

Much has yet to be learnt about this rapidly declining species. Its habitat requirements have not been systematically surveyed and there are very few data on specific edaphic conditions. Although a poor competitor, B. compressus appears to tolerate frequent anoxia within the root zone and is therefore abundant in inundated habitats. The extent to which populations in southern England have declined in response to falling water-tables and/or because of eutrophication requires further investigation.

References 
  • Brewis, A, Bowman, P, Rose, F. 1996. The Flora of Hampshire. Harley Books and Hampshire and Isle of Wight Wildlife Trust, Colchester.
  • Graham, G.G. 1988. The Flora and Vegetation of County Durham. The Durham Flora Committee and the Durham County Conservation Trust.
  • Halliday, G. 1997. A Flora of Cumbria. Centre for North-West Regional Studies, University of Lancaster. Smith, P.H. 1984. The distribution, status and conservation of Juncus balticus Willd. in England. Watsonia 15: 15-26.
  • Westhoff, V. & van Leeuwen, C.G. 1962. Catapodium marinum (L.) Hubbard, Scirpus planifolius Grimm en Trifolium micranthum Viv. op Goeree. Gorteria 1: 33-38.
Citation 
Walker, K.J. & Braithwaite. (Date accessed). Species account: Blysmus compressus. Botanical Society of the British Isles, www.bsbi.org.uk.

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