ft 3 DATABASE AND ATLAS OF AQUATIC VASCULAR PLANTS THE BRITISH ISLES Part I : Species Accounts NRA ITE National Rivers Authority Project Record 352/2/N&Y fG'S-C ' NRA 352/2/N&Y NATIONAL RIVERSAUTHCJRITY D atabase ami-*rtflas o-f aquatlp-^7ascu 1 ar p la n ts i j AJXC -tfT 1 so . 00 Database and Atlas of Aquatic Vascular Plants in the British Isles Part I: Species Accounts C D Preston and J M Croft Research Contractor: Institute of Freshwater Ecology Monks Wood Abbots Ripton Huntingdon Cambridge PE17 2LS National Rivers Authority Rivers House Waterside Drive Almondsbury Bristol BS12 4UD Project Record 352/2/N&Y ENVIRONMENT AGENCY 136210 Commissioning Organisation National Rivers Authority Rivers House Waterside Drive Almondsbury . Bristol BS12 4UD Tel: 01454 624400 Fax: 01454 624409 ® National Rivers Authority 1995 . All rights reserved. No part of this document may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the National Rivers Authority. The views expressed in this document are not necessarily those of the NRA. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein. Dissemination Status Internal: Limited Release External: Restricted Statement of Use This document provides information on the occurrence and distribution of aquatic plants in Britain and provides a valuable source of data fro NRA staff.. Research Contractor This document was produced under project 352 by: Institute of Freshwater Ecology Monkswood Abbots Ripton Huntingdon Cambridge PE17 2LS NRA Project Leader The NRA's Project Leader for Project 352 was: John Hogger - Northumbria and Yorkshire Region . Additional Copies No further copies of this document are available. Both volumes of the Project Record will incorporated into a book to be published in Spring 1996 as "An Atlas of Aquatic Vascular Plants in Britain and Ireland" by Harley Books, Colchester, Essex. Project Record 352/2/N&Y CONTENTS PAGE SUMMARY 1 INTRODUCTION 3 SPECIES ACCOUNTS 5 REFERENCES 303 INDEX 351 SUMMARY - VOLUME I The objectives of the Atlas and Database of Aquatic Plants Project are to develop a database of the distribution of aquatic plants in Britain and Ireland, and to prepare summaries of the data for publication. The project is funded by the Joint Nature Conservation Committee, the National Rivers Authority and the NERC Institute of Terrestrial Ecology. This report consists of draft accounts of the families, genera, species and subspecies covered by the project. The habitat and reproductive biology of each species is outlined, trends in its British and Irish distribution discussed and its world distribution is summarised. Additional notes on other topics of interest are sometimes provided. The text should be read in conjunction with the distribution maps, Volume II. The text will be revised in the light of any comments received from referees and the modified text, maps and necessary introductory material and illustrations will be submitted to Harley Books for publication as a book, Aquatic Plants in Britain and Ireland 1 INTRODUCTION The objectives of the Database and Atlas of Aquatic Plants Project are : I- ■ to develop a database on the distribution of aquatic plants; 2 to prepare summaries of the data for publication as a book Aquatic Plants in Britain and Ireland. The project is jointly funded by the Joint Nature Conservation Committee (JNCC), the National Rivers Authority (NRA) and the Institute of Terrestrial Ecology (ITE). It builds on the existing records of aquatic plants held by the Biological Records Centre (BRC) at ITE Monks Wood. An outline of the project is provided in an earlier report (Preston et a/., 1993). Distribution maps of the taxa covered by the project are also included in that report. This report consists of text to accompany these maps. The species covered by the project are those vascular plants in Britain and Ireland which characteristically grow in permanent fresh or brackish water. They include submerged macrophytes, free-floating species and emergents which are rooted in permanent water but have aerial leaves. The project excludes plants which are not usually found in permanent water but which are rooted in floating masses of vegetation, or occur in seasonally flooded sites, fens or bogs. The dividing line between land and water is not clear-cut, but is marked by seasonal and non-seasonal fluctuations and more gradual changes. It cannot, therefore, be expected that there will be a clear division between terrestrial and aquatic plants, and many species have actually evolved to exploit the various transition zones between land and water. Many species undoubtedly qualify for inclusion under our criteria, but decisions about borderline cases are inevitably somewhat arbitrary. As the dividing line is so fuzzy, we have had no hesitation in occasionally including borderline species when it was convenient to do so: we have, for example, included both Ranunculus hederaceus and R. omiophyllus in order to provide an account of all the species in Ranunculus Subgenus Batrachium. During the preparation of the text, it has become clear that a few changes need to be made to the list of species covered by the project to bring it into line with the criteria outlined above. A number of species are mapped by Preston et aL (1993) but have subsequently been dropped and are not included in this report: these are Carex appropinquata, C. nigra, Equisetum palustre, Hydrocotyle vulgaris, Iris versicolor, I. x robusta, Lythrum salicaria, Mentha aquatica, Ranunculus lingua and Typha x glauca. Most of these can be found in permanent water but are not sufficiently frequent in this habitat to qualify for inclusion. However, we have added Carex recta, Hydrocotyle ranunculoides, Ranunculus reptans and R. x levenensis. There are only three species of vascular plants which grow in sea water in our area, namely Zostera angustifolia, Z marina and Z. noltii. These are not covered by this project but accounts of all three are provided by Stewart et aL (1994). The numbering of the families and the genera follows Kent (1992). The scientific names of 3 British and Irish taxa are taken from Kent (1992) and the English names from Stace (1991). Synonyms are not given in the accounts of individual taxa, but synonyms which have been in recent use are included in the index. The text which follows gives a brief account of each family covered by the project. This attempts to set the British and Irish representatives in the context of the family as a whole. The accounts of the genera and species in the family follow. The generic accounts also attempt to set our species in the world context. If certain information is common to all the members of a genus this is usually given in the generic account rather than repeated under each species. The generic accounts are therefore variable in length, and tend to be short if there is pnly one aquatic plant in the genus in our area. It is important that the reader should realise that the account of the genus and that of the species should both be read to obtain all the information about the species. The first paragraph of each species account describes the habitat in Britain or Ireland. The altitudinal limit is given, and ’lowland’ denotes altitudes less than 300 m. The altitudinal limit may not be given explicitly for plants which are clearly confined to the lowlands (e.g. certain coastal species). The next paragraph outlines the reproductive biology and the third paragraph discusses any historic trends in the distribution in Britain and Ireland. If a species is thought to be under-recorded, this is mentioned here. The world distribution is described in the fourth paragraph. Other information may be added in a fifth paragraph. The species accounts presented here are final drafts. Some points which still require clarification are identified in bold in the text, and full details of a few references still need to be added. The maps and text, together with introductory material and illustrations, will be submitted to Harley Books on 10 July 1995 for publication as a book Aquatic Plants in Britain and Ireland. 4 \ 3. ISOETACEAE The Isoetaceae is a small and taxonomically isolated family of pteridophytes. In addition to Jsoetes, it includes only one other genus, Stylites, which is endemic to the Peruvian Andes. 3/1. Isoetes L. Isoetes is a genus of c. 100 species, of which 11 are recognised in Europe. They have linear leaves (or ’sporophylls’) arising from a bulb-like structure or ’corm\ The base of the sporophyll is expanded and contains a sporangium. The large female megaspores and the smaller male microspores are borne in sporangia on separate sporophylls on the same plant. The spores are released as the sporophylls die and decay. Both male and female prothalli develop within the spore walls, the mobile male gametes emerging from the microspores to effect fertilisation. The simple structure of Isoetes offers few characters to the taxonomist, and this (coupled with extreme phenotypic plasticity) means the taxonomy of the genus has always been difficult. Recent evidence indicates that interspecific hybridisation can take place in the genus, and that some species have arisen as fertile allopolyploids (Hickey et al., 1989). There are still a number of taxonomic problems to be resolved even in Europe. Three Isoetes species are known in Britain and Ireland, two of which are aquatic (/. echinospora, I. lacustris) and one terrestrial (I. histrix, a rare Mediterranean-Atlantic species restricted in our area to S.W. England and the Channel Islands). Plants which are apparently intermediate between I. echinospora and I lacustris have recently been found in Britain (Camus et al., 1988). Their taxonomic status has still to be elucidated and they are not considered further in this account. The aquatic Isoetes species exemplify the ’isoetid’ growth habit. Isoetids have a rosette of short stiff leaves (often with extensive internal air spaces) arising from a short stem. This growth habit is found in a number of other British and Irish species in unrelated families: Subularia aquatica (Brassicaceae), Littorella uniflora (Plantaginaceae)* Lobelia dortmanna (Campanulaceae) and Eriocaulon aquaticum (Eriocaulaceae). These plants are so similar in habit that they are sometimes confused by field botanists. Isoetids are found in nutrient-poor habitats, often in areas which are disturbed by wave-action. They are slow-growing, evergreen plants. A high proportion of their biomass is accounted for by their roots, which are often mycorrhizal (Farmer & Spence, 1986). They are unable to utilise bicarbonate ions as a source of C02, and are thus restricted to using C02 in the sediment in which they grow. It has recently been shown that Isoetes species and Littorella uniflora possess Crassulacean Acid Metabolism (CAM), a photosynthetic pathway more usually associated with desert succulents (Keeley, 1982, Farmer & Spence, 1985). This pathway allows carbon dioxide to be accumulated at night in malic acid, which is then released in the day and used in photosynthesis. Desert plants are thus able to minimise water loss by opening the stomata at night. The CAM pathway allows Isoetes and Littorella to recycle C02 released into the leaf lacunae at night by respiration, a valuable adaptation for plants which characteristically grow in habitats where the inorganic carbon content is low (Boston, 1986). Isoetes lacustris L. Quillwort I. lacustris is a characteristic species of oligotrophic lakes. It usually grows over rocky substrates with skeletal soils or over base-poor sands or clays, being absent from silty mud. Scattered plants often grow in shallow water at the edge of lakes, where they are frequently accompanied by Littorella uniflora and Lobelia dortmanna. However, the species is usually more frequent at greater depths and it can be the dominant (and sometimes the only) macrophyte at depths below 1.5-2.5 m. It has been recorded in water as deep as 6 m at Loch Lundie (West, 1905). The freshwater sponge Spongilla lacustris is often a conspicuous associate in these deep water stands (Spence, 1964). In addition to natural lakes, / lacustris has also colonised artificial reservoirs and the Muirtown Basin of the Caledonian Canal. It is recorded from sea-level to 825 m at Ffynnon LIyffaint. Little information is available about the reproduction of /. lacustris in Britain or Ireland, but the presence of small plants at the edge of lakes suggests that establishment from spores is not infrequent. Laboratory studies of the closely related I macrospora Durieu in N. America showed that neither megaspores nor microspores required a cold treatment for germination (Kott & Britton, 1982). A high proportion of megaspores germinated (an average of 87%), the maximum germination being reached in 45 days or less. Megaspores from dried plants failed to germinate. Isoetes lacks any means of vegetative reproduction. I. lacustris was clearly under-recorded in the Atlas of the British Flora (Perring & Walters, 1962), presumably because it is most abundant in deeper water and scattered plants are easily overlooked when growing with Littorella unijlora in the shallows. It is probably still under­ recorded in areas which have not been covered by intensive surveys. There is little evidence for any major decline in /. lacustris in Britain or Ireland. Like other isoetids, it is extinct at some of its more easterly sites, which are now eutrophic, and other such populations are probably vulnerable (Farmer & Spence, 1986). It formerly grew, for example, at Bomere Pool but, like Lobelia dortmanna, it is now extinct there (Sinker et al., 1985). It has been suggested that I. lacustris and other isoetids have declined in Scandinavia as a result of acidification. The evidence is discussed by Rjarslett & Brettum (1989), who conclude that it is extremely scanty. There is much clearer evidence of a decline in The Netherlands, where acidification has followed the increased input of ammonium into water bodies in recent years. Add reference here. /. lacustris is frequent in Europe north of c. 53°N; it extends south as scattered populations to N. Spain (Jalas & Suominen 1972). 1. lacustris sensu lato (including the N. American species I. macrospora and I occidentalis, which may be conspecific with it) has a circumboreal distribution. Isoetes echinospora Durieu Spring Quillwort Over much of its British and Irish range /. echinospora grows, like I. lacustris, in oligotrophic lakes; it has also been found at the edges of slow-flowing rivers and in pools. It occurs over a wide range of nutrient-poor substrates including rocky'and stony areas, base-poor sands and gravels, sandy mud or silt and peaty deposits. In Shetland it favours a finer substrate than /. lacustris and apparently prefers the sheltered S. and W. sides of lochs (Scott & Palmer, 1987); this is probably true elsewhere in Britain. Although it usually grows in oligotrophic sites, /. echinospora has occasionally been found in eutrophic lakes, notably Llyn Llygerian and Llyn Llywenan in Anglesey (Seddon, 1965). Here it is found in areas where the growth of emergent species is restricted by rocky outcrops or by heavy wave action. I. echinospora has colonised an artificial reservoir in Cumbria, flooded gravel pits at Capel Bangor and disused clay pits in Dorset and Devon. It ascends from sea-level to 470 m at Llyn Glas. Little or no information is available about the reproduction of I. echinospora in Britain or Ireland. Experimental studies in N. America have shown that a cold period of 4°C for 12 weeks stimulates megaspore germination, but even with such a treatment total germination was very low (15%). Spores subjected to shorter pretreatments and control samples failed to germinate as did megaspores from dried specimens. Microspores germinated without a cold pretreatment but a 4°C pretreatment for 12 weeks resulted in a higher percentage germination (Kott & Britton, 1982). It would be interesting to know if /. echinospora from Britain and Ireland has similar requirements. Although I. echinospora often has more flaccid, gradually tapering leaves than /. lacustris, the two species can only be identified with certainty by microscopic examination of the megaspores. Although /. echinospora has been known from [add first record here) it is almost certainly under-recorded both because Isoetes plants are themselves often overlooked and because I. echinospora may be assumed to be /. lacustris or not noticed when the species are growing together. Fossil evidence indicates that I echinospora has been present in Britain from the late Weichselian onwards, and long-term persistence through the Flandrian has been demonstrated at some sites (Godwin, 1975). The botanical records are insufficient to provide any evidence of change in its distribution since it was first reported in 18??. I. echinospora has a similar European range to I lacustris: it is frequent in N. Europe and present as very scattered populations south to N. Spain and Greece (Jalas & Suominen, 1972). Isoetes echinospora sensu lato is a very variable and taxonomically complex species which has a circumboreal distribution, with isolated occurrences in Barbados and Chile. I. echinospora and I. lacustris are ecologically similar in Britain and Ireland, and can grow together (Stokoe, 1978). In Scandinavia I. lacustris "occurs mainly in oligotrophic to mesotrophic lakes" whereas I. echinospora "is a ubiquitous species of clayey riverside habitats and intermittently dried-out mudflats", also occurring in dystrophic lakes, clear-water lakes, turbid eutrophicated sites and in slightly brackish water (Rarslett & Brettum, 1989). This suggests that I. echinospora has a much wider habitat range in Scandinavia than in Britain or Ireland, with a correspondingly clearer distinction between /. echinospora and I. lacustris. In Scandinavia I. echinospora tends to occur in shallower water than /. lacustris (although there is considerable overlap between the two species). Unfortunately, critical observations on the depth at which /. echinospora grows in Britain are not available. 7