f t 3 DATABASE AND ATLAS OF AQUATIC VASCULAR PLANTS THE BRITISH ISLES Part I : Species Accounts ITE NRA National Rivers Authority Project Record 352/2/N&Y ' NRA 352/2/N&Y fG 'S-C NATIONAL RIVERSAUTHCJRITY Database ami-*rtflas o-f a q u a tlp -^ 7 a s c u 1 ar p la n ts i j A JXC -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 o f 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 o f the genus and that o f 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.