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Mike Grant writes on keying

Who's afraid of botanical keys?

by Mike Grant, Editor of The Plantsman. Formerly Senior Botanist, Royal Horticultural Society Garden Wisley
Have you ever spent ages flicking through illustrated gardening encyclopaedias trying to identify an unknown plant? Ever wished you had a tame expert who you could identify everything for you? Well, there is a DIY option if you have access to them - botanical keys.
There comes a time when most plant enthusiasts will want to attempt identification of a plant that can't be nailed by matching it with a picture in a book. This normally requires the use of books that contain botanical keys, but these can be a rather daunting prospect when encountered for the first time. In this brief article I hope to introduce you to the concept of keys and find ways round the commonest problems.
A key is nothing more than a series of pairs of contrasting statements (couplets) that lead, by a process of elimination, to the name of a plant. It is a bit like a multiple choice test, but easier because there are only two choices available at each step. It sounds simple but novices can be put off if they fail to reach an answer or get stuck halfway. Here are some of the sticking points and ways round them.
Look at the structure of the key before you start and make sure you know where the contrasting statements lie in the key. You may find that the second part of the couplet is over the page from the first part they may be numbered or lettered 1/1, 1a/1b, 1.1/1.2, a/aa or any variation of these. Sometimes the couplets are not labelled but just indented under each other; in this case the second statement of the couplet is indented to the same degree from the margin but may be several lines below the first statement.
Keys often use technical terms for parts of the plant. However, most books containing keys also have a glossary so you can look up the meaning of the terms. If you can't find a glossary then use one from another book. Always read the text immediately preceding the key, such as the genus description, as it will often contain useful tips and put the terminology into context. Wrong turning Make sure you read both statements comprising the couplet before you decide which lead to follow. Some keys are better than others at providing a good contrast between the statements e.g. leaves densely hairy / leaves moderately hairy is rarely easy to determine. If you can't decide on which lead to follow then try both and see what happens. The wrong lead will usually come up with a very unlikely answer or the subsequent couplets will start to bear no resemblance to the plant. In this case go back to the point where you diverged. Likewise, if you think you've gone wrong then return to the last couplet where you were certain.
Wrong key, wrong country
Ensure that the key you are using is likely to cover the plant in question. A key to Chinese lilies will not identify an American species. This is where horticulturists face greater problems than wild plant botanists. If you don't know the provenance of the plant in question then deciding on the right key can be a rather hit-and-miss affair. Gardeners are at a further disadvantage in that the plants they grow are often hybrids or selections that blur the usual botanical distinctions. If you think your plant is not a pure species or you don't know the country of origin then try a key to cultivated species. Remember that the majority of cultivated lilies are complex hybrids for which there are no keys.
Wrong season
Some keys, either through bad design or because it is unavoidable, ask questions about characters that are only visible at certain times of the year. For instance, a key may ask about flower characters and fruit characters. You can either persevere and try different leads, or be patient and record the relevant details for later use.
The final corroboration
Obtaining a name from the key is not the end of the exercise. You must check that the species given as the answer agrees with your plant. This is why botanists depend so much on dried, pressed specimens in a herbarium. If you don't have access to reliably identified specimens then you will need to check your answer against published descriptions and illustrations - and hope that it matches!
Some books and websites with keys to lilies:
Flora of North America Editorial Committee (eds.) (2002) Flora of North America North of Mexico. Volume 26. Oxford University Press, Oxford.
key to 22 species of lily found in North America. Flora available online at
Haw, S.G. (1986) The Lilies of China. B.T. Batsford, London.
key to 37 species of lily found in China, the more recent Flora of China recognises more species. Huxley, A. (ed.) (1992) The New Royal Horticultural Society Dictionary of Gardening. The Macmillan Press Ltd, London.
key to about 90 cultivated species and hybrids of lily. The key only goes down to groups of species, not individuals. Walters, S.M. et al (eds.) (1986) The European Garden Flora. Volume I. Cambridge University Press, Cambridge.
key to 52 cultivated species of lily. Wu, Z. & Raven, P.H. (eds.) (2000) Flora of China. Volume 24 (Flagellariaceae through Marantaceae). Science Press, Beijing & Missouri Botanical Garden Press, St. Louis.
key to 55 species of lily found in China.