Species Dossierpallavicinia Lyelli
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Pallavicinia lyelli Veilwort PALLAVICINIACEAE SYN: Pallavicinia lyellii (Hook.) Caruth. Status UK BAP Priority Species Lead Partner: Plantlife International & RBG, Kew Vulnerable (2001) English Nature Species Recovery Programme Status in Europe - Vulnerable 14 10km squares UK Biodiversity Action Plan (BAP) These are the current BAP targets following the 2001 Targets Review: T1 - Maintain populations of Veilwort at all extant sites. T2 - Increase the extent of Veilwort populations at all extant sites where appropriate and biologically feasible. T3 - If biologically feasible, re-establish populations of Veilwort at three suitable sites by 2005. T4 - Establish by 2005 ex situ stocks of this species to safeguard extant populations. Progress on targets as reported in the UKBAP 2002 reporting round can be viewed online at: http://www.ukbap.org.uk/2002OnlineReport/mainframe.htm. The full Action Plan for Pallavicinia lyelli can be viewed on the following web site: http://www.ukbap.org.uk/UKPlans.aspx?ID=497. Contents 1 Morphology, Identification, Taxonomy & Genetics................................................2 2 Distribution & Current Status ...........................................................................3 2.1 World ......................................................................................................3 2.2 Europe ....................................................................................................3 2.3 Britain .....................................................................................................4 2.3.1 England .............................................................................................5 2.3.2 Wales ................................................................................................9 2.3.3 Scotland.............................................................................................9 3 Ecology & Life Cycle........................................................................................9 4 Habitat Requirements ................................................................................... 10 4.1 The Landscape Perspective....................................................................... 10 4.2 Communities & Vegetation ....................................................................... 13 4.3 Summary of Habitat Requirements ............................................................ 13 5 Management Implications .............................................................................. 13 6 Threats / Factors Leading to Loss or Decline or Limiting Recovery........................ 14 7 Conservation Measures.................................................................................. 16 7.1 Surveying, Monitoring & Recording ............................................................ 16 7.2 Research ............................................................................................... 16 8 References .................................................................................................. 16 9 Acknowledgements ....................................................................................... 17 10 Contacts................................................................................................... 18 11 Links........................................................................................................ 18 1 1 Morphology, Identification, Taxonomy & Genetics Veilwort Pallavicinia lyelli is a mat-forming, thalloid liverwort of humid, often shaded, habitats on a variety of acidic substrates. The plants are usually dark green with a translucent, shining appearance (see Figure 1), especially in shaded situations, but can be much paler when more exposed. The plants are said to be aromatic - Schuster (1992) describes them as having a ‘pronounced, rather fishy smell.’ Thalli do not normally exceed 4cm in length, although individual thalli up to 7cm are known from a site in East Sussex. Thalli are often prostrate and attached to the substrate by brown rhizoids, or they can be somewhat ascending, especially in favourable conditions. Fresh thalli are often rather undulate and have a crisp texture. When handled they make a sound that Paton (1999) likened to that of ‘best quality tissue paper’. Branches arise from the ventral surface of thalli, which are occasionally furcate. Margins are normally entire but can have a slightly dentate appearance due to the presence of papillae, especially on male plants. Veilwort has a prominent, clearly defined costa with a central conducting strand, which is sharply differentiated from the one-layered lamina (see Figure 2). The conducting strand appears dark in transmitted light and as a pale, almost white line in herbarium material. Figure 1 – Pallavicinia lyelli at Wimbledon Common. (Photograph by Gill Stevens). Veilwort is dioecious. Male plants, which tend to be smaller than females, can be recognized by antheridial lamellae that occur on either side of the costa. Female plants bear laciniate involucres along the median line of the costa – normally one or two from around the middle of the thallus onwards. Sporophytes are uncommon, especially as only one sex is present at some sites. Gametangia are visible from the late summer onwards and sporophytes are usually produced during May in Britain. 2 Figure 2 – Pallavicinia lyelli. (With kind permission of Fred Rumsey). Although Veilwort is relatively easily recognised once known, it is superficially similar in appearance to a number of other species of the Metzgeriales, particularly Moerckia hibernica and Pellia spp. with which it is sometimes associated. The central conducting strand usually suffices to separate Pallavicinia lyelli from both. From Pellia it can also be distinguished by the unistratose lamina, the presence of marginal papillae and antheridial and involucral lamellae. Moerckia is more similar but the antheridial lamellae cover the dorsal surface of the costa in that plant, whereas they tend to be restricted to a line on each side of it in Veilwort. Habitat is also an important consideration as Moerckia grows in quite base-rich conditions in which Veilwort is never found. Some old records from predominantly limestone areas may therefore refer to misidentified Moerckia. 2 Distribution & Current Status 2.1 WORLD Veilwort has been reported from all continents except Antarctica, although occurrences from tropical Asia, Australasia and Oceania are doubtful and have been referred to P. pseudolyellii by Schuster (1992). In the holarctic, Veilwort shows oceanic or sub-oceanic tendencies and becomes increasingly montane with decreasing latitude (ibid). In Eastern North America it is common in wet hollows in woodland (J. Duckett in Hill et al, 1992) and in wet sandstone canyons (Schuette, pers. com.). In the southern hemisphere it is reported from tropical regions of South America and northern and central Africa. 2.2 EUROPE Veilwort has a sub-oceanic distribution in Europe (Hill & Preston, 1998), where it is widespread but nowhere common. The species is classified as vulnerable throughout Europe as a whole. The status of Pallavicinia lyelli in each country in Europe, where 3 known, is shown in Table 1. It is recorded from beside wet, shaded streams and bogs and on wet sandstone rocks, in which habitat it grows in the High Weald of southeast England. Table 1 - Country by country status of Pallavicinia lyelli across Europe. (*Country codes are taken from Flora Europaea as of 1964. IUCN threat categories as revised by the European Committee for Conservation of Bryophytes, 1995). COUNTRY* STATUS STATUS NOTES SOURCE(S) Au AUSTRIA Endangered ECCB (1995). WITH LIECHTENSTEIN Az AZORES Rare ECCB (1995). Be BELGIUM Not ECCB (1995). WITH LUXEMBOURG threatened Br BRITAIN Vulnerable Gradual decline since 1950s Church et al INCL ORKNEY, ZETLAND & notably in the north, most (2001). ISLE OF MAN probably in response to land drainage. Recorded at just 10 sites since 1970. Cz CZECHOSLOVAKIA Vanished Extinct in this country. ECCB (1995). Ga FRANCE Endangered – ECCB (1995). Rare Ge GERMANY Vulnerable ECCB (1995). Hb IRELAND Vulnerable ECCB (1995). BOTH NORTHERN IRELAND & THE REPUBLIC OF IRELAND Ho NETHERLANDS Rare ECCB (1995). Hs SPAIN Rare ECCB (1995). WITH GIBRALTAR & ANDORRA, EXCL BL It ITALY Endangered Conti et al (1997). Ju JUGOSLAVIA Extinct SERBIA SLOVENIA Lu PORTUGAL Vulnerable ECCB (1995). Po POLAND Endangered ECCB (1995). Su SWEDEN Vanished Extinct in this country. ECCB (1995). 2.3 BRITAIN Veilwort is at the northern edge of its European range in the UK. Its British distribution is concentrated in southern England. A number of significant populations have also been recorded from west Wales and the Somerset Levels and there have been scattered records from East Anglia, and northern England as far north as Cumbria. There are a small number of unconfirmed 19th century records from southern Scotland, and Veilwort has recently been discovered in Renfrewshire. Its apparent absence from the Midlands and much of eastern England is probably real, while the lack of records from parts of southwest England is puzzling. Veilwort has historically been reported from about 46 sites in the UK since its first discovery some 200 years ago. The number of known extant sites in the UK now stands at 20 (14 in England, five in Wales and one in Scotland), recorded from a total of 23 vice-counties. Although eight of these populations are recent discoveries (post 2001), this probably represents a significant decline. Veilwort still