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Potamogeton compressus

Taxonomy 

The correct name for this species is Grasswrack Pondweed, Potamogeton compressus L., but the name P. compressus has, in the past, sometimes been used to refer to what is now called P. friesii, so care should be taken with literature records prior to about 1950. Older books often used the name P. zosterifolius Schumacher (Clapham, Tutin & Moore 1989).

Chromosome No.: 2n = 26 (Stace 2010).

Potamogeton compressus

Photography: A.J.Lockton

Identification 

Confusions about the identification of P. compressus were largely resolved by J.E. Dandy & Sir George Taylor in the mid-20th century, and definitive descriptions are given by Preston (1995). The keys in older works are unreliable. It is easy to confuse P. compressus with either P. friesii or P. acutifolius, and specimens should be collected whenever it is legal and responsible so to do.

Distribution 

Grasswrack Pondweed occurs throughout Europe and Asia as far east as Japan, according to reports on the internet, but not in North America (Preston & Croft 1997). In Britain it occurs in numerous sites in England, but in just one lake in Scotland and one canal in Wales. A report compiled from the Threatened Plants Database, listing its known sites in 2008 is available for downloading here: (pdf 246kb).

BSBI Hectad Map 

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

Status 
  • Origin: native. It was first recorded in Britain by John Ray in the River Cam in Cambridge in 1660 (Crompton 2001).
  • Rarity: Nationally Scarce in Britain (Stewart, Pearman & Preston 1994)
  • Threat: in the New Atlas (Preston, Pearman & Dines 2002) it is described as having declined over the last 150 years, and it is currently listed as Endangered (Cheffings & Farrell 2005). However, analysis of the data on the TPDB shows that the decline is less severe than previously thought. It turns out that P. compressus moves about, creating the impression of a decline. It was slightly more abundant in the mid-20th century than before or afterwards, due to the abandonment of canals, but it has never been a common plant.
  • Conservation: it is a Priority Species on the UK Biodiversity Action Plan. Most counties that have it consider it an axiophyte, as it only occurs in clear water.
Ecology 

Preston & Croft (1997) describe its habitat as still or slowly flowing, calcareous, mesotrophic water. It is found in rivers, canals, ditches and lakes in the lowlands. Rodwell (1995) lists it as occurring in A11 Potamogeton pectinatus- Myriophyllum spicatum vegetation.

Further Work 

Because of its ability to colonise new sites, it is important to continue to search for it and record it carefully. Studies into its ecology are needed, especially for the sites where it has persisted for many years, as these appear to be exceptionally rich and important sites for many other aquatic species. As a BAP species, it often receives ‘interventions’ of various sorts, including introductions and translocations. These should be documented on Conservation Evidence (see Markwell & Halls (2008) for an example).

References 
  • Crompton, G. 2001. Catalogue of Cambridge Herbarium and Flora of Cambridgeshire. www.mnlg.com/gc/ (accessed 2001).
  • Markwell H.J. & Halls J.M. 2008. Translocation of a nationally scarce aquatic plant, grass-wrack pondweed Potamogeton compressus, at South Walsham Marshes, Norfolk, England. Conservation Evidence 5, 69-73.
  • Preston, C.D. 1995. Pondweeds of Great Britain and Ireland. Botanical Society of the British Isles, London.
  • Preston, C.D. & Croft, J.M. 1997. Aquatic Plants in Britain and Ireland. Harley Books, Colchester.
Citation 
Lockton, A.J. (Date accessed). Species account: Potamogeton compressus. Botanical Society of the British Isles, www.bsbi.org.uk.

Pontederia cordata

Taxonomy 

Pontederia cordata L., Pickerelweed, has various synonyms:

  • Narukila cordata (L.) Nieuwl.
  • Pontederia angustifolia Pursh.
  • P. sagittata C.Presl.
  • P. lancifolia Muhl. Nutt.

It is the only member of the Pontederiaceae likely to be found growing in the wild in Britain. Other members of this small family are not hardy enough to survive the winter. One other species from this family, the Water hyacinth (Eichhornia crassipes), is occasionally cultivated in gardens. The Pontederiaceae are in the order Commelinales of the monocots.

Chromosome No.: 2n = 16 (Stace 2010).

Pontederia cordata

Photography: A.J.Lockton

Identification 

It is a rhizomatous, perennial aquatic. It has two kinds of leaves, submerged, sessile leaves with linear blades, and either emerging or floating leaves with lanceolate to cordate blades. The emerging leaves are 10-20 cm across bright glossy green on long fleshy petioles. It flowers during the summer, with showy spikes of 100 or more violet-blue flowers held well above the leaves. Each flower is about 2-3 cm across and zygomorphic.

Pontederia cordata

Photography: A.J. Lockton

Distribution 

It is native in North and South America, from Canada to Argentina. However, it has naturalised widely outside its native range and is officially a noxious weed in Australia and South Africa. In Britain it was first recorded in Wimborne, Dorset in 1949, though the Flora of Dorset states ‘rarely surviving for long,’ perhaps implying that this site has now gone. Records exist for England, Scotland, Wales and Ireland, but it is most often found along the south-coast of England, particularly in Surrey and Sussex.

BSBI Hectad Map 

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

Status 
  • Origin: not native in Britain.
  • Rarity: not rare.
  • Threat: it appears to be increasing, but this is likely to be because of deliberate introductions, rather than to a natural spread.
  • Conservation: like many non-native plants, it is sometimes considered a threat to biodiversity, and is eradicated; but there is no real evidence for any damage.
Further Work 

Nothing appears to be known of which of the many described varieties from the New World grow in the Great Britain and Ireland.

Can all of the three of the tristylous morphs be found?

Is Pontederia cordata hardy enough to survive the hardest winters?

References 
  • Horn, C.N. & Haynes, R.R. 1987. Typification of Pontederia and its Linnaean species names (Pontederiaceae). Taxon 36 (3), 621-625. eFloras (2008). Published on the Internet http://www.efloras.org [accessed 27 April 2008] Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
Citation 
Groom, Q.J. (date accessed). Species account: Pontederia cordata. Botanical Society of the British Isles, www.bsbi.org.uk.

Nuphar lutea and N. pumila

Taxonomy 

Name: Nuphar lutea (L.) Sm. Yellow Water-lily

Synonyms: Nuphar lutea L.

Name: Nuphar pumila (Timm) DC. Least Water-lily

Synonyms: Nuphar xintermedia Ledeb.

Name: Nuphar xspenneriana Gaudin. Hybrid Water-lily

Synonyms: Nuphar lutea var. pumila Timm.

All 2n = 34

In the UK there are two genera that belong to the Nymphaeaceae – Water Lily family: Nuphar (Yellow Water-lilies) and Nymphaea (White Water-lilies).

Nuphar has two native species: Nuphar lutea and N. pumila (Least Water-lily) and a hybrid between the two N. xspenneriana (Hybrid Water-lily). The introduced species N. advena (Spatter-dock) has been recorded from the UK. Beal (1956) considered N. advena and N. pumila to be subspecies of N. lutea.

ADD PICTURE

Identification 

When flowering separating Nuphar and Nymphaea is unmistakeable, but problems may arise with vegetative material.

Nymphaea leaves are usually + circular with anastomising veins and a circular petiole; Nuphar leaves are longer than wide and have reticulate veins that never meet up at the margins and triangular petioles.

More difficulty emerges in separating the species and hybrids of Nuphar and this is detailed in the Plant Crib.

BSBI Hectad Map 

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

Nuphar lutea

Nuphar pumila

Nuphar xspenneriana

Lycopodiella inundata

Taxonomy 

Lycopodiella inundata (L.) Holub. is also known as Lycopodium inundatum L.

Its common name is Marsh Clubmoss.

Chromosome No.: 2n = 156 (Stace 2010).

Lycopodiella inundata

Photography: M. Cotterill

Distribution 

The main populations in Britain are found in the south of England, in the New Forest and on heaths in Hampshire and Surrey. It also occurs in Scotland, in bogs and on the margins of lakes. Between these two centres of population there are a few isolated localities such as North Wales and Cumbria. It was once more widespread, but it disappeared from many sites in England prior to 1930 as a result of drainage and agricultural intensification. Its highest recorded altitude is 390 m at Llyn Cwmffynnon (v.c. 49) by Trevor Dines in 1999 (Pearman 2004).

It has a curious distribution globally, in scattered locations throughout much of Europe, and is on both the east and west coasts of North America (mapped by GBIF as Lycopodium inundatum), where it is rare.

BSBI Hectad Map 

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

Status 
  • Origin: it is considered native to Britain and Ireland. The first British record was by Christopher Merrett (1666) at Putney Heath in Surrey.
  • Rarity: Nationally Scarce in Britain and rare in Ireland.
  • Threat: currently listed as Endangered in the JNCC’s Red List due to its Change index of -0.65.
  • Conservation: it is a Priority BAP plant in the United Kingdom.
Ecology 

It is a short-lived perennial of bare peat in mires and heaths. Rasmussen & Lawesson (2002) studied its contrasting ecology in England and Scotland and concluded that the closest vegetation type for it in England was M16 Erica tetralix-Sphagnum compactum heath, whereas in Scotland it occurred in M15 Trichophorum cespitosum-Erica tetralix heath and M29 Hypericum elodes-Potamogeton polygonifolius soakways. In its lowland English sites it is often maintained by drastic management activities to produce bare soil, whereas on the edge of peaty lochs in Scotland the harsh conditions and fluctuating water levels produce this habitat naturally.

Further Work 

Rasmussen and Lawesson (2002) suggested that the more natural Scottish populations should receive more attention than the putatively archaeophytic populations in southern England, claiming this would be more likely to be successful. Detailed studies on the success rate of conservation programmes might therefore prove interesting.

References 
  • Headley, A.D. Lycopodiella inundata (L.) Holub. In Stewart, A., Pearman, D.A., & Preston, C.D. 1994. Scarce Plants in Britain. JNCC, Peterborough.
  • Merrett, C. 1666. Pinax Rerum Naturalium Britannicum.
  • Pearman, D.A. 2004. Altitudinal Limits of British and Irish Vascular Plants. BSBI.
  • Rasmussen, K.K. & Lawesson, J.E. 2002. Lycopodiella inundata in British plant communities and reasons for its decline. Watsonia 24, 45-55.
Citation 
Lockton, A.J. (date accessed). Species account: Lycopodiella inundata. Botanical Society of the British Isles, www.bsbi.org.uk.

Impatiens capensis

Taxonomy 

Impatiens capensis Meerb. (the type specimen was mis-named, as it was thought by Meerburgh to have originated in South Africa (Burtt 1938)) has the smallest distribution of the three neophyte Impatiens species found in the wild. It is considered by Hultén & Fries (1986) to be a synonym of I. noli-tangere subsp. biflora [Walt.] Hult. in England and France.

Common names: Orange Balsam, Jewelweed, Lady’s earrings, Spotted Touch-me-not.

Synonym: I. biflora Walt.

Hybrids: None known in Europe. However, for the U. S. Pacific Northwest, Zika (2006) records hybrid Impatiens pacifica Zika - a cross between I. capensis and the local rare endemic I. ecalcarata.

Chromosome No.: 2n = 14 (Stace 2010); 2n = 20 (Clapham et al. 1987).

Impatiens capensis

Photography: P. Day.

Identification 

Mature leaves: 7-10 teeth with shortly decurrent base. Stems: hollow, succulent, translucent and branching to third order in mature plants.

Impatiens capensis

Photography: P. Day.

Distribution 

Occurs in much of lowland England and eastern South Wales, where it has colonised the banks of many streams and rivers and has followed the canal network - its explosive capsule dehiscence and positive seed bouyancy aiding its hydrochorous dispersal (Trewick & Wade 1986). Maximum recorded altitude is 167 m near Wetton, mid-channel on the River Manifold in the Peak District National Park (v.c. 39) (J. Hawksford, pers. comm.).

BSBI Hectad Map 

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

Status 

Origin: neophyte from eastern North America. Thought to have escaped from cultivation in Surrey, and first noticed in 1822 by the R. Tillingbourne at Aldbury; with the first published record in 1829 on the R. Wey at Guildford (Louseley 1976). The species is now also naturalised in Denmark, Finland, France, Germany, the Netherlands and Poland.

Rarity: common and widespread.

Threat: none; however, it continues gradually to increase its spread. Change Index (New Atlas) of +0.71.

Conservation: a non-axiophyte. It is a naturalised invasive species which has no conservation value within the British flora. The plant is designated as having little or no economic or ecological impact by the Environment Agency and UK Water Framework Directive.

Ecology 

It is a well established annual, usually found in small stands on marshy ground next to slow-moving water, often growing amongst coarse herbs in both open and shaded sites. It germinates from what can be a persistent seed bank (Perglová et al. 2009) from early March to mid-April, and flowers from early August to late September. A typical plant has both cleistogamous (closed and self-pollinated) and protandrous chasmogamous flowers, and is pollinated by bees, hoverflies and wasps. In eastern North America, an important pollinator is also the Ruby-throated Hummingbird. Rodwell (1991-2000) defines it as a component of W5 Alnus glutinosa woodland and S24 Phragmites australis tall-herb fen. However, in the Thames Valley it is commonly found within S14 Sparganium erectum swamp along riverbanks; OV32 Myosotis scorpioides communities in the dryer zones of fluctuating streams and associated ponds; and W6 Alnus glutinosa woodland along the upper reaches of Chilterns chalk streams. It has also been recorded in Shropshire in W6 and OV32.

Further Work 

Little has been published in Britain with respect to the ecology of I. capensis - the only known account is by Bennett (1873). However, Maps Scheme records show a gradual extension northwards in range since the 1960s; and climate change might not only facilitate further extension of both the present altitude and northern latitude limits of the plant, but also modification to its currently relatively benign status. Regular monitoring of the plant’s status would be a worthwhile task. I would be very interested to learn if anyone has had experience of germination and seedling growth experiments for the species, particularly as seed stratification timing seems so difficult to judge with any accuracy. The Balsam Carpet (Xanthorhöe biriviata) moth is known to be phytophagous on I. capensis. Has anyone any knowledge of other fauna so inclined?

Email Peter Day

References 
  • Bennett, A. W. 1872. On the Floral Structure of Impatiens fulva, Nuttall, with especial reference to the Imperfect Self-fertilized Flowers, Botanical Journal of the Linnean Society, 13, 147-153.
  • Burtt, B. L. 1938. Bulletin of Miscellaneous Information (Royal Botanic Gardens, Kew), 1938 (4), 161-163.
  • Lousley, J. E. 1976. Flora of Surrey. Newton Abbott, Devon: David & Charles.
  • Perglová, I., Pergl, J., Skálová, H., Moracová, L., Jarošík, V. & Pyšek, P. 2009. Differences in germination and seedling establishment of alien and native Impatiens species, Preslia, 81, 357-375.
  • Trewick, S. & Wade, P.M. 1986. The distribution and dispersal of two alien species of Impatiens waterway weeds in the British Isles. In: Proceedings of the International European Weed Research Society/Association of Applied Biologists 7th Symposium on Aquatic Weeds. Loughborough, 351-356.
  • Zika, P. F. 2006. Impatiens pacifica (Balsaminaceae), a new hybrid jewelweed from the Pacific Northwest coast of North America, Novon, 16, 443-448.
Citation 
Day, P. (date accessed). Species account: Impatiens capensis. Botanical Society of the British Isles, www.bsbi.org.uk.

Crassula helmsii

Taxonomy 

Crassula helmsii (Kirk) Cockayne is correctly called, in English, New Zealand Pigmyweed, but it is also often known as Australian Swamp Stonecrop.

Synonyms:

  • Crassula recurva (Hook. f.) Ostenf. non N.E. Br.
  • Tillaea recurva (J.D. Hook.) J.D. Hook.
  • Tillaea helmsii Kirk

Chromosome No. 2n = 36 (Stace 2010).

Crassula helmsii

Photography: A.J.Lockton

Distribution 

It is native to Australia and New Zealand. The GBIF map shows it to have a restricted world distribution in south Australia and parts of NW Europe. It is a lowland plant: maximum recorded altitude is 345 m (Llyn Pendam, Cardiganshire).

BSBI Hectad Map 

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

Status 
  • Origin: neophyte. A native of Australia and New Zealand that was introduced to Britain in the early 20th century and was first recorded in the wild in 1927 (in Essex).
  • Rarity: common in England & Wales; local in Scotland; rare in Ireland.
  • Threat: in the 1980s and ‘90s it was believed to be spreading very rapidly in the British Isles, but more recent authors (e.g. Crawley 2005) have observed that the increase was not so dramatic; and the Maps Scheme data shows that it is no longer among the top 100 most rapidly spreading species in Britain.
  • Conservation: it has been said that Crassula helmsii would outcompete rare native species (e.g. Defra 2003) and, in consequence, many organisations attempt to eradicate it. There is, however, no published evidence for this point of view.
Ecology 

A perennial semi-aquatic plant that grows on the margins of ponds and lakes. It is notorious for regrowing from small fragments, which makes it difficult to eradicate. Like many non-native species it can become very abundant for short periods, especially in sites that have become eutrophic and where the native flora is already under stress. In less enriched conditions it is not so vigorous, and it tends to form sparse stands in shallow water. It favours light shade and is easily damaged by wave action, which explains why it is most commonly found in small ponds.

Further Work 

The issue of invasive alien species is an emotive one and, even within the field of scientific research, it is difficult to find neutral studies of species such as this. Owing to the high cost of eradicating such plants, it would make sense to have a clearer understanding of their ecology and the effects - if any - that they really have on native species. There have apparently been no studies yet of its phytosociology or its interaction with animal species. Preston & Croft (1997) suggested that its seeds may not be viable in this country - which may be worthy of further investigation. Crassula helmsii flowers late into the winter and may provide a useful source of nectar; studies of its value to bees and other invertebrates might therefore prove interesting and topical. No evidence has yet emerged for it outcompeting rare native plants.

 

Case Study: Brown Moss, Shropshire.

Brown Moss was once famous for its rare plants and heathland habitats, which earned it every conservation designation going, including SSSI, Ramsar and cSAC status. But since the 1960s it has been deteriorating slowly, and a host of characteristic species have become extinct there, including Pilularia globulifera, Sparganium natans, Baldellia ranunculoides, and Luronium natans. The cause is very obviously a lack of grazing, leading to succession to woodland. In the 1990s Crassula helmsii became very abundant around one of the pools at Brown Moss and efforts have been made to control it.

Crassula helmsii

The photograph (above) shows a half-hearted attempt to spray it out, which coincided with the disappearance of Lythrum portula and Hypericum elodes from the same areas - but did little to harm the Crassula. In 2003 a more serious effort was made to dig up and remove all the Crassula and the ‘contaminated’ mud.

Crassula helmsii

The photograph (above) shows the outcome of that effort a year later. In many places only Persicaria amphibia and Crassula helmsii survived. This effort coincided with the brief reappearance of both Baldellia ranunculoides and Luronium natans - almost certainly from buried seed that had been uncovered by these operations. Unfortunately, only three plants germinated, and none of them set seed. This case study shows how difficult it is to eradicate Crassula helmsii without also damaging rare and more vulnerable native species. It also shows the value of active site management which can restore habitat and facilitate the return of lost species by uncovering the buried seedbank. Unfortunately, it shows that focusing too much on alien species can distract from essential conservation work, and even harm the native species that are supposedly being protected. The current status of Brown Moss is that almost all the features of conservation interest are now absent or damaged, and it arguably no longer warrants cSAC or SSSI status.

If you have experience of Crassula helmsii control - whether successful or not - they can usefully be contributed to Conservation Evidence.

References 
  • Crawley, M.J. 2005. The Flora of Berkshire. Brambleby Books, Harpenden.
  • Defra. 2003. Review of non-native species policy. Department of Environment, Food & Rural Affairs, London.
  • Preston, C.D. & Croft, J.M. 1997. Aquatic Plants in Britain and Ireland. Harley Books, Colchester.
Citation 
Lockton, A.J. (date accessed). Species account: Crassula helmsii. Botanical Society of the British Isles. www.bsbi.org.uk.

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

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.

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).

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.

Pilularia globulifera

Taxonomy 

Name: Pilularia globulifera L.

Family: Marsiliaceae

Common name: Pillwort.

It has no synonyms.

Chromosome No.: 2n = 26 (Stace 2010).

Pilularia globulifera

Identification 

This is a tiny fern, about 8cm tall, which is easily recognised by the characteristically unfurling leaves and the large (3 mm), round sporocarps, if present (Page 1997; Stace 1997). The only similar fern in Europe is P. minuta, which occurs in the western Mediterranean but not in Britain (Tutin et al. 1993). It is perhaps most easily confused with seedlings of Juncus, or submerged Juncus bulbosus plants; specimens should always be collected or photographs taken if a new site is found.

 

Distribution 

It is endemic to Europe, occurring in most Western European countries and extending eastward as far as Poland and Italy (Fl. Europaea). It is widespread throughout Britain and Ireland, excepting only the Northern Isles, but restricted to suitable habitats, which are limited to about ten scattered clusters.

BSBI Hectad Map 

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

Status 
  • Rarity: Nationally Scarce (Stewart et al., 1994) in Britain. Rare in Ireland. 
  • Origin: native throughout.
  • Threat: in the New Atlas (Preston, pearman & Dines 2002) it is given a Change Index of -0.03, representing a small decline; but it is one of those species that is always well recorded, and the Change Index over-compensates for recent recording levels. The map shows it has been lost from nearly half of all its known sites. Cheffings & Farrell (2005) list it as Near Threatened.
  • Conservation: Pillwort is one of the few species that is widely considered a universal axiophyte - i.e. it is always important for conservation even in areas where it is relatively common.
  •  
Ecology 

Jermy, in Stewart, Pearman & Preston (1994) gives a detailed account of its habitat in shallow water on pond margins, in poached wet grassland and even, occasionally, in mires. Populations can vary greatly from year to year, often responding quickly to low water levels leaving exposed bare substrate. Jermy (ibid.) reports that spores can develop through the gametophyte stage to produce new sporophytes in just 17 days, which makes it an opportunistic coloniser. He questions whether the sporocarps remain dormant for long periods, or whether new habitat is colonised by fresh spores from nearby populations. In the north of Scotland it seems to occupy quite a different niche. Most of the records are for the sides of rivers and lakes where, perhaps, the scouring effect of running water creates the open conditions it requires.

Further Work 

We have no real idea of whether this species is in decline or the change index is not reliable for an historically well-recorded species, or for a plant that is mobile. A detailed study of its historical range and populations is needed. A controversial aspect of the conservation of Pillwort has been the readiness of organisations to plant it. It has been introduced or re-introduced to numerous sites in Scotland including a place on the Island of Rum where it is may not have occurred naturally. At Dowrog Common in Pembrokeshire there was a reintroduction attempt that appears to have failed, but the plant re-appeared years later when appropriate management was introduced (S.B. Evans, pers. comm.). this leaves a nagging doubt about whether it really is a native population or not, and the reintroduction attempt is now seen as unfortunate. A study of the genetics of this population might usefully resolve the question.

References 
  • Page, C.N. 1997. The Ferns of Britain and Ireland, 2nd edition. Cambridge University Press, Cambridge.
Citation 

Lockton, A.J. (date accessed). Species account: Pilularia globulifera. Botanical Society of the British Isles, www.bsbi.org.uk.

Luronium natans

Taxonomy 

Luronium natans

Accepted name: Luronium natans (L.) Raf., Floating Water-plantain.

Synonyms: Alisma natans L.; Elisma natans (L.) Buchen.

Chromosome diploid no.: 2n = 42 (Stace 2010).

Identification 

This is one of the most awkward plants in Britain for identification, as Its leaves are extremely variable in shape, with those submerged up to half a metre long (pers. obs.) and ribbon-shaped, or just a centimetre across and almost round (Stace 1997). It is rarely in flower. The key feature for identification is the presence of stolons which, in the absence of flowers, is the only reliable diagnostic feature that separates it from Baldellia ranunculoides and Alisma plantago-aquatica.

Distribution 

According to Cook et al. (1975) and Preston & Croft (1997), L. natans is restricted to Europe and is declining throughout its range. Cook (ibid.) however, observed that it appeared to be expanding its range in Britain; and the New Atlas (Preston, Pearman & Dines 2002) seems to confirm that with a slight recorded increase overall, and recently confirmed records for Ireland and Scotland.
 
Given the problems of identification, little is certain about this species. It was first recorded in Scotland, for instance, by the normally reliable William MacGillivray (Withering’s Arrangement 1841); but that record is often discounted on the grounds that it was not found there again for a long time.
 
The core populations in Britain are in the lakes of Mid-Wales and the Shropshire Meres, with outlying populations in the canal network and in heathland pools as far away as Dowrog Common in Pembrokeshire and South Weirs in the New Forest. There are always suggestions that it is introduced when it crops up in new sites - for example, at Calthorpe Broad and Potter Heigham in Norfolk (Preston & Croft 1997) - but there is little direct evidence of that. It is a difficult plant to grow, and canal ecologists have tried to introduce it to new sites with little success.

BSBI Hectad Map 

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

Status 

Origin: native, probably throughout the British Isles; but because populations in Scotland, southern England and Ireland have tended to be temporary, it is sometimes treated as an introduction outside its core areas.
 
Rarity: with fewer than 100 hectads in Britain, it should be classed as Nationally Scarce. There is only one known site for it in Ireland, so it is rare in the Republic.
 
Threat: it is listed as Least Concern by JNCC (Cheffings & Farrell 2005). BSBI records seem to show a slow increase in the total populations (Lockton 2009).
 
Conservation: UK BAP priority species. This is one of the most important plants in Britain, for both nature conservation and genetic conservation reasons. The British Isles holds a large proportion of the world population, and it only grows in the best quality water bodies. Being such a demanding plant for its habitat, it is extremely difficult to cultivate or successfully introduce to new sites, meaning that existing sites must be protected.
 
Legal: Luronium natans is protected in UK law under Schedule 8 of the Wildlife & Countryside Act; which makes it illegal to uproot or damage plants, or to collect them without a licence.
 

Ecology 

Luronium natans

 

 

 

 

 

 

 

The importance of L. natans to conservation is matched by its highly specialised ecological requirements which could be summarised as ‘clean water.’ It grows in depths of up to 2 m in oligotrophic lakes in Wales (Trueman, Morton & Wainwright 1995) or in shallower mesotrophic water bodies. It requires high levels of light (Hill et al. 1999), so algal growth, shade and turbidity can be fatal to it.

The sites where it occurs include oligotrophic to mesotrophic lakes and pools - often those with fluctuating water levels, as it tends to flower and fruit prolifically when exposed on bare mud. It is mostly a lowland plant, reaching its altitudinal limit at 450 m in Llyn Bugeilyn in Montgomeryshire (v.c. 47) (Pearman 2004). It also still occurs in several canals, but it disappears when a canal is restored to navigation and boat traffic increases above a very low level. Such low usage sometimes occurs on the most uninspiring stretches of canal in urban areas.

Further Work 

The most important thing is to continue to collect good quality, validated records of this species. Its distribution in Scotland and Cumbria is still uncertain, and the origin and persistence of outlying populations is a matter of much interest and speculation.
With a BAP species such as this, a lot of conservation work is happening, such as introductions and translocations. These should be documented on Conservation Evidence, if not written up elsewhere.

References 
  • Cook, C.D.K., Gut, B.J., Rix, E.M., Schneller, J. & Seitz, M. 1974. Water Plants of the World. W. Junk, The Hague.
  • Hill, M.O., Mountford, J.O., Roy, D.B., & Bunce, R.G.H. 1999. Ellenberg’s indicator values for British plants. HMSO.
  • Lockton, A.J. 2009. Luronium natans update. BSBI Recorder 13, 12-16.
  • Lockton, A.J. & Whild, S.J. 2005. Rare Plants of Shropshire, 3rd ed. Shropshire Botanical Society, Shrewsbury.
  • Pearman, D.A. 2004. Altitudinal Limits of British and Irish Vascular Plants. BSBI.
  • Preston, C.D. & Croft, J.M. 1997. Aquatic Plants in Britain and Ireland. Harley Books, Colchester.
  • Trueman, I.C., Morton, A. & Wainwright, M. 1995. The Flora of Montgomeryshire. Montgomery Field Society & Montgomeryshire Wildlife Trust, Welshpool.
Citation 

Lockton, A.J. (date accessed). Species account: Luronium natans. Botanical Society of the British Isles, www.bsbi.org.uk.

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