The Wildflower Key
The wild flower guide that I use most often is 'The Wildflower Key' by Francis Rose. Although it is possible to just look at the (excellent) illustrations to identify the wild flowers you find, you'll get more out of it if you use the keys to help you make the correct identification.
Keys can seem intimidating if you haven't used them before, but once you get over the initial learning curve, you quickly realise how useful they are. A key will actually make you look at the the way the flower is put together, and teach you to notice features you might otherwise overlook such as the arrangement of the leaves on the stem.
A few tips to using keys:-
- Find the glossary, and mark the place with a finger or bookmark (a scrap of paper works fine!).
- Don't guess the meaning of unfamiliar words. That's what the glossary is for.
- When learning how to use a key, try keying out a plant that you know.
- Know (remember) that the first part of the keys is about splitting apart different large groups of plants, which is mostly about how the flower is put together.
- Try writing down the steps you have taken in a column down a sheet of paper. When you come to a question and can't decide which choice is correct, start a side row across the page (in other words go both ways). (Try not to do this too much, otherwise your paper will just become a maze).
Once you have an answer, check the description, particularly noting what sort of habitat the plant is found in. If you're on a sand dune, and the habitat is given as swamp or fen, you might want to go back to check your identification.
New Flora of the British Isles
The New Flora of the British Isles by Clive A Stace is more of a definitive reference work than a field guide, but one no serious botanist should be without. It covers all vascular plants growing wild in the British Isles. It is the successor to "Flora of the British Isles" by Clapham, Tutin and Warburg. Possibly a little intimidating for beginners, but full of a wealth of detail.
Grasses
Grasses by C Hubbard has long been the standard work on grasses in the British Isles. A key, and excellent, detailed black and white line drawings are invaluable when identifying grasses.
Sedges of the British Isles
Sedges of the British Isles by AC Jermy, DA Simpson, MJY Foley and MS Porter is my book of choice for identifying sedges. It is published by the BSBI and has keys, detailed species descriptions, line drawings and distribution maps.