Dichotomous keys

The exercises we will perform these days will mainly be with dichotomous keys. These keys can only be constructed when the final groups (taxa or parts thereof) are unit-groups characterized byt... 

Really practicable keys are comparatively rare and dichotomous keys should be in accordance with the following Ten Commandments t... 

Relation of number of couplets (consisting of two leads) vs. number of taxa keyed out In a dichotomous key which divides the group into equal (50%—50%) blocks the equation isi y 2 to the power x or x 2log y (x number couplets y number taxa). Thus for 8 taxa one has to pass 3 couplets, but for 32 taxa only 51 (In fact 6 questions reap. 10, as both leads need to be read carefully ) The total... 

Bergey s Manual of Determinative Bacteriology is the standard reference for laboratory identification of bacteria. Dichotomous keys, which incorporate information... 

Figure 134 Dichotomous keys for identification of brewing spoilage microbes.

Dichotomous key Taxonomic key used to identify organisms, composed of paired (either-or) statements describing characteristics. 

In the early stages, but not exclusively, and as in most other taxonomic groups, identification was based on dichotomous keys. Kreger-van Rij (1984), Kurtzman and Fell (1998) and Barnett et al. (20(X)a) presented keys based on physiological tests only or physiological tests together with... 

Computerized keys are usually multiple-entry keys (MEKs) that allow the user to ask any question in any order. Overall, MEKs are superior to printed or dichotomous keys. Some of the problans highlighted previously for predefined printed dichotomous keys can be avoided. Using MEKs, identifications may be quick and easy, but a single mistake or difference in the observed results may lead to errors. Therefore, identification keys should be used with care. However, MEK are very useful, for example, to search for a set of properties in a given data-base. 

In 1990, while starting a biodiversity study of the yeast flora in wet and dry forests of central Africa, it became obvious that identification using conventional methods was barely possible. The standard physiological tests were tedious, slow and difficult to interpret unambiguously, and the identification of isolates using the classical dichotomic keys was very difficult. As a consequence. 

Not only are concise descriptions clearer, they enable the Flora to be more compact. Hooker was clearly aware that a more compact Flora is produced more quickly and cheaply. However, a problem with this concise approach was that, although the species are usually grouped with shared characters, the descriptions are often not particularly diagnostic and frequently not usable by themselves to separate similar species. In many cases, accurate identification is only achievable with reference to a comprehensive, well-curated herbarium. This is compounded by the fact that only synoptic (not dichotomous) keys are included. Nevertheless, the Flora of British India was a revelation for a descriptive Flora in English. Although much of the taxonomy has been subsequently refined, it is a good example of the benefits of producing a usable product warts and all . In the absence of an alternative (until very recently) it has been much used and copied by later workers. 

Dichotomous keys, either of the bracketed or indented type, provide a means of identification to all taxa in the Flora area from family level down to infraspedfic rank. Descriptions of the taxa generally cover the range of morphological variation as found within the Flora area and are intended to be concise and diagnostic rather than comprehensive or comparative, their aim being to serve as a check on the keyed out taxa. In the excursion flora format of FWTA, much of the descriptive information is included within the keys, the actual species descriptions themselves being very condensed. 

The book can be used and enjoyed equally well at home or in the field. The informative introduction provides a readable account of dragonfly ecology and helps to put what follows into context. Field trips can be planned in advance at home with reference to the regional guides. These accounts are especially useful when visiting sites for the first time or those that are situated far from home, when on holiday for example. Larvae and exuviae are particularly difficult to identify to species level in the field because the diagnostic features may be obscured by debris or they may be too small to be seen with the naked eye. Users of the book are recommended to confirm their identifications at home and a dichotomous key is provided as the most suitable means of securing an accurate identification. 

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