1 Small details are important
When carrying out species identification, it is often the small details that are important to distinguish similar species – for example, whether a sedge flower has two stigmas or three. Details of the flower are possible to see clearly with a hand lens. Yet the characteristics that distinguish separate species of fungi often relate to the shape and size of their spores or other microscopic features, such as cells on the gill edge. Various other groups of organisms also require very close examination in order to identify separate species, such as the two common Bathyporeia amphipods (crustaceans that live on the seashore). These appear identical apart from the presence or absence of a small, backwardly projecting spine which is visible only under a microscope.
Going beyond the microscope, there are species-identification techniques that are based on the chemical composition of the organism, particularly its genetic material – its DNA – which is present in every cell. These techniques can be highly effective at detecting even tiny differences between species. And some of them can also be used to develop molecular phylogenies showing a detailed family tree for each species.
The third technique described here is automated species identification. The computer analyses an image or a sound recording and compares it with a large database of derived information from correctly identified examples of each species. This technique has the potential for rapid species identification and has become increasingly accurate over recent years.
Figures 1 and 2 provide another example of two different species that are almost identical apart from some tiny differences. The images shown are of two very similar species of sedge that often grow in similar conditions and can be separated by the number of their stigmas (the white female part of the flower that collects pollen grains). Figure 1 (a) is a close-up of the slender tufted sedge (Carex acuta), which has pairs of stigmas. While Figure 2 (b) is the lesser pond sedge (C. acutiformis), which has stigmas grouped in threes. The difference is clearly visible with a hand lens.