EEB337H1 - Families of Vascular Plants

Printed Keys


These are the traditional tools for plant identification that botanists have been using since the time of Lamarck and A. P. de Candolle, i.e. the late 18th century (Radford et al., 1974; Voss, 1952). Keys like this (whether strictly binary or employing multiple choices as well) are the only kind of identification tool that can be readily reproduced in printed form. The Orchids of Wisconsin web site provides a good example of an interactive indented, binary key for the identification of orchid genera most of which also occur in Ontario. Another example is Thonner's analytical key to the families of flowering plants (Geesink et al., 1981). A third example is the key to Ontario genera of the Ericaceae (s.str.) shown below. It was generated automatically by the DELTA program CONFOR.EXE using the TOKEY directive. Note that it is not a strictly binary key (see character 9). The authors of the DELTA system believe that restricting keys to exclusively binary choices is unecessary, given the inherently multistate nature of many characters used in identification.

Ontario Ericaceae Genera key generated by the DELTA program CONFOR.EXE from dataset with 20 characters assembled by M. Svoboda (BOT 307F, 1996)

 
1(0). Fruit berry.......................................... 2
      Fruit dry capsule.................................... 6
 
2(1). Ovary Superior....................................... 3
      Ovary Inferior....................................... 4
 
3(2). Leaf persistent (leaves stay attached during the winter 
           but wither)........................ Arctostaphylos
      Leaf evergreen (no change, leaves  ready  for use  next
           season)................................... Epigaea
 
4(2). Leaf base rounded or wedge-shaped............ Vaccinium
      Leaf base tapered.................................... 5
 
5(4). Leaf deciduous............................. Gaylussacia
      Leaf evergreen.............................. Gaultheria
 
6(1). Leaf flat............................................ 7
      Leaf inrolled (i.e. margins revolute)................ 9
 
7(6). Leaf entire............................... Rhododendron
      Leaf crenate......................................... 8
 
8(7). Flower white.............................. Chamaedaphne
      Flower red.................................. Phyllodoce
 
9(6). Leaf tip pointed (with or without mucro)..... Andromeda
      Leaf tip blunt................................... Ledum
      Leaf tip round.................................. Kalmia

What is the main drawback of printed keys like this one, or others that you have used on field trips or in labs in this and other courses? Well, for one thing, they start with one particular question. If you are unable to answer it, you have to follow both leads. Suppose, for example, you were called on to use the Wisconsin orchid key to identify an orchid inflorescence that had been removed from the field. You might not be able to tell whether the leaves were present on the intact plant when the inflorescence was removed. As a result, you would have to pursue the possible identifications under both A ("Leaves absent ... at flowering") and AA ("Leaves present at flowering"). Similarly, using the Ericaceae key above, if you had neither fruits nor flowers to work with you would have to explore four different leads (2, 3, 4, 6), and even then might not be certain of the identification you made.

As described elsewhere at this site, an alternative approach is to implement a polyclave, or "multiple entry key." You can compare the Ontario Ericaceae key above with a polyclave version of the same data by clicking HERE to use PollyClave logo.


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Please send your comments to tim.dickinson@utoronto.ca; last updated 06-May-2008