Some plants can be pretty difficult to pin down their identification and a specialist book can prove useful. For many groups there are few choices and the ones shown here are the standard works. All except the volume on ferns are paperback so eminently portable, not that anyone would take them into the field unless looking specifically at these groups of plants.
Again, all except the ferns volume have keys that lead to informative species pages, but they can be difficult to work with if not familiar with both their intricacies and botanical terms. Grasses and British Sedges are especially good specialised and detailed guides, they may only contain line drawings, but these are accurate and work well.
If only a single volume is to be chosen, then the Collins guide is the one to have if you can’t afford the rather pricey but better Francis Rose guide. The drawings in the Collins guide are coloured (beware the accuracy of these) so it is a more attractive volume, but its vegetative key is pretty good too.
Books from my shelves:
Guide to the Grasses, Sedges, Rushes and Ferns of Britain and Northern Europe, Richard Fitter, Alistair Fitter, illustrated by Ann Farrer. Collins, 1984. ISBN 0 00 219136 9
British Sedges, A.C. Jermy, T.G. Tutin. Botanical Society of the British Isles (BSBI), 1977 reprint, first published 1968.
British Ferns, Ron Freethy. The Crowood Press, 1987. ISBN 0 946284 33 4
Grasses, C.E. Hubbard, revised by J.C.E. Hubbard. Penguin, third edition 1984, first published 1954. 3579 10 864