Identification of moulds is based almost entirely on the structures bearing spores and on the spores themselves. Therefore it may be useful for the reader to go back to the beginning and reread the sections in chapters 1 and 2 describing the different kinds of moulds and their anatomy. The process of identification usually involves keys, specialized flow-charts leading to the name of the organism at hand. There are many kinds of keys in use; we present two here, dichotomous keys and picture keys.
The most common means of identifying moulds is by the use of a dichotomous key, a very clever device presenting a series of alternatives for consideration. A glance at any of the keys that follow will serve as a demonstration. In the key for Group I, for example, there are two choices at number 1, two at number 2, two at number 3, etc., on up to number 14. Each pair of choices represents a decision to be made about the mould which is under examination. In number 1 one has to decide whether the mould's spores are composed of one cell or divided by cross-walls into two or more cells. If they are one-celled, the key sends one on to consider the choice in number 2; if they are more than one-celled, one must go to 12. Eventually the series of decisions will lead to a name.
Most books the reader may wish to use will have dichotomous keys that work in the same way as the ones here. But beware; some authors introduce a third or even fourth, fifth, or sixth choice in their keys that may not be noticed as first!
It is difficult to recommend one or even a few books on identification. The best I can do is direct the reader to a few texts as a good starting points. Ainsworth, Sparrow, and Sussman (1973) and Arx (1981) offer keys to most of the groups of fungi you are likely to encounter. If the mould under examination appears not to be an ascomycete, basidiomycete, or zygomycete, try starting with Barron (1968), Barnett and Hunter (1987), or Carmichael et al. (1980). Fungi forming spores in pycnidia can be identified in Nag Raj (1993) and Sutton (1980). For zygomycetes, start with O'Donnell (1979). Domsch et al. (1980), a monumental work treating all fungi known to occur in soil, includes keys, illustrations and extensive literature citations. It is an indispensible book for anyone doing serious work with moulds. De Hoog and Guarro (1995), Gravesen et al. (1994), Samson, et al. (1995), and St-Germain and Summerbell (1996) are beautifully illustrated books, the first and last dealing with fungi of medical interest and the others with fungi found on foods and other human-associated materials. Wang and Zabel (1990), dealing with fungi isolated from utility poles, is a very useful reference for wood-inhabiting fungi. It contains extensive keys and illustrations. The latest addition to our library of mould identification books is The Genera of Hyphomycetes by Seifert, Morgan-Jones, Gams and Kendrick (2011). This monumental volume of almost 1000 pages treats its subject in great detail, illustrating and describing hundereds of species. If you really want to get into the subject, this is the place to go.
Keys to sixty common genera of moulds
Two approaches are taken to identification in this section: a set of dichotomous keys and a set of picture keys. Which you choose depends upon your individual preference. Some people are verbal in nature and do best when everything is written out; these people usually prefer dichotomous or other types of textual keys. Others are visual and prefer to match what they see to an image. You may even find you do best with a combination of the two.
THE DICHOTOMOUS OR TEXT KEYS
The dichotomous keys are designed to work like the mind of an experienced mycologist, eliminating the most common or most expected fungi first and relegating the less common ones to the end. These are composed of keys to several groups of genera. Group I contains the most commonly encountered genera, group II those that are a little less common, and group III those that are less common yet, and so on down to the end. To use the key, start with the key to group I. If you are satisfied that the fungus you are trying to identify is not there, try the key to group II. If that does not work, go to Group III, and so on. The chances are greatest, of course, that the mould you want to identify is in group I, since these are the commonest of all moulds. If your fungus is not among the 60 genera in the whole key, you will have to turn to more complete or specialized books, such as those listed above or in the bibliography.
It should be pointed out that all identifications should be checked against the appropriate description and illustration following the key. It may also be necessary to turn to the references given there. Fungi from one group may be identified incorrectly in the key to another group and only the description and illustration will reveal the mistake. For example, Paecilomyces of group II will key out to Penicillium in group I, but this problem will only be discovered when checking the descriptions and illustrations.
THE PICTURE KEYS
These keys are arranged in the same way as the dichotomous keys: that is, the first set of pictures illustrates the most comonly encountered moulds. Those in the second set are also common, but not quite as common as those in the first group. To use the keys, browse over the first group to see if your unknown specimen matches one of the pictures. If you think it fits one of them, click on the picture for further information. If the fit is not very good, go back and try again. If the unknown is not in Group I, go on to Group II.