Keys are one way to find the name of a fungus. There are other ways and there are various kinds of keys. This is a simple explanation designed to accompany some field keys that I have developed to try to help myself and others identify New Zealand fungi. Such keys are far from perfect and you need to read what follows to understand the strengths and weaknesses of various keys.
Limitations on all keys
Clearly keys can only identify species that have been fully described. In parts of the world where almost all the species in a particular genus are known, for example in Japan, Scandinavia and parts of North America, keys can achieve quite high accuracy levels. Good field keys should achieve about 80% accuracy if properly tested and used. In places where there are many as yet undescribed species, such as is the case for Mycena in New Zealand, an accuracy level of 30 – 40% might be expected.
Keys only work in the area for which they were designed. If you purchase a European key, even a very good one like Funga Nordica, you will get an accuracy of less than 5% if you use it in New Zealand, because almost all the species that occur here are unknown in Sweden or Denmark. The only place where it might work, would be if you collect a fungus under a Birch tree or a European pine species.
The advent of gene sequencing has brought to light a number of what are known as ‘cryptic species’. That is species that have a unique sequence but there is no fruit body, description or any other details. Conventional keys cannot cope with these.
Types of keys and their advantages and limitations
Taxonomic keys
Professional mycologists are trained to apply certain standards to the design of keys. Species are recognised on the basis of criteria, for example they must have at least one visible character that is different from another species. Others require one macroscopic and one microscopic character to differ. These standards are mostly not explicitly set out in published keys. Characters commonly used in other kingdoms such as defining species on the basis of whether they can successfully interbreed, are difficult to apply to many fungi.
Taxonomists place closely related species together and then prepare a dichotomous key. This involves preparing a list of either/or questions that reflect the past evolutionary changes that gave rise to the different species. Changes might for example be some fundamental chemical reaction such as the ability to break down lignin or cellulose. Testing for the enzymes that allow lignin to be broken down is clearly challenging, so professional mycologists use proxy values, if a fungus can digest lignin it leaves behind cellulose which is a pale colour and thus we have ‘white rotters’. Most keys divide the Polypores in to white and brown rotters.
Some evolutionary changes are however much harder to find proxy values for and taxonomists like to be precise, so we have many keys with characters for which you will need a compound microscope with a times 1000 magnification and you will need to develop skills in preparing microscope sections and staining tissues.
Taxonomic keys can deliver high accuracy identifications but very few people can use them successfully. Their accuracy is high but their productivity is low.
Field keys
The origin of field keys is hard to pin down. They are undoubtedly centuries old and probably started as a way of recording how local people identified edible and poisonous plants. Their objective is to get you to an answer as simply and reliably as possible, but frequently this has very little to do with the fundamental evolutionary changes that resulted in a particular species differing from others. They tend to be focussed on identifying common and significant species. Typically, such keys have been prepared by amateur mycologists and they have also largely used the dichotomous keys approachof paired questions. They try to cover all the species that occur in a particular country or region or habitat and this is usually stated in the introduction. But beware, publishers have been known to translate keys into to other languages and leave out the introduction.
Field keys deliver relatively quick answers for many more people but the level of accuracy suffers. Their productivity is high but they only have medium accuracy.
Key Designs
Dichotomous keys
A traditional dichotomous key consists of a series of questions, the questions should be sharp so the user is in no doubt about which step they should choose. The questions are usually in pairs called couplets. For example:
| 1. Cap black | 2 |
| 1. Cap another colour, not black | 3 |
This couplet gives you a clear choice and this is the sort of choice that is typical of field keys.
Taxonomic keys are often forced in to difficult early choices because they are dealing with fundamental evolutionary changes. An example is:
1. Clamp connections present 2
1. Clamp connection absent 27
This kind of couplet poses several challenges, you must get out your microscope and search the whole fungus. If you find clamp connections that is fine, but if you do not, you are never quite sure if it is a failure of your technique or whether they are truly absent. You also don’t know quite where to look. Many taxonomists are helpful and have couplets such as:
1. Clamp connections at the base of the basidia 2
1. Basidia without clamp connections at their base 27
This directs you where to look, but you still have to get out the microscope, cut a good section and use an appropriate stain.
One of the major drawbacks of dichotomous keys is that, if you are unable to answer any particular question, then you cannot easily proceed to the later questions and that invalidates the remainder of the key. Multiple option questions and synoptic keys have been developed to ease this problem.
Multiple option keys
One simple innovation that reduces the number of steps and shortens the key is to group couplets that are different options for the same basic question. A good example is Karl Soop’sCortinariod Fungi of New Zealand (2017) that has several combined steps e.g. Key G step 30:
30. Cap white or pale ochre 31
30. Cap with a distinct apricot to pinkish hue C. persicanus
30. Cap mahogany-brown to blackish C. picoides
Synoptic keys
Dichotomous keys are designed so that the questions have to be answered in a particular sequence, like decision trees. It is the user’s responsibility to find the answers to each of the couplets. Synoptic keys start from the idea that the user will know certain things about the fungus and these can be fed in to the key. Geoff Kibby has been a leading proponent of this approach in the UK. To use such a keyyou need to eamine the fungus against a coding sheet. Here is an example from a Russula key:
A for a red cap
J because you can peel the cuticle off the cap with your nails.
K for a white stem
N because the cap is 30 – 100 mm diameter
P because it has white spores
S because the flesh tastes acrid.
You then look up the code AJKNPS and discover that there are only 5 Russula species that meet these easy criteria that you can observe. A dichotomous key to separate these five is then provided and that contains some more complex questions involving spore sizes.
Synoptic keys lend themselves to computerisation and Fungimap’s Funkey to the Genera of Australian Agarics is a good example of a computerised synoptic key. If you use one always enter the characters that are strong and clearly defined, don’t be tempted to follow all the questions in order. You will find a simple synoptic key for Pluteus on the FUNNZ website.
Synoptic keys are easy to use and have a relatively high accuracy and are quick and easy to use for some genera. They place a high burden on those preparing the key both in selecting the characters to use and then coding all the species for all the characters.
Other identification methods
Ask an expert
Many people first learn how to identify fungi from an ‘expert’. The credentials of ‘experts’ vary widely. Some, like the staff at PDD, are professional mycologists, some are people laden with experience and tradition, a polish grandmother or an Italian great aunt. In a few countries there are trained people, mostly pharmacists, who have a responsibility to identify fungi for the public and thus prevent collectors from poisoning themselves. Changes in society are reducing the number of ‘experts’ quite dramatically. Finding an expert who can identify the mushroom you have just found is itself a challenge. They never seem to be there when you need them. In theory the internet should help a lot, but most experts have day jobs and the number of fungi that can be reliably identified from photos is very small, of the order of 2%of macrofungi. But this a very reliable method, albeit with very low productivity.
Photo IDs
If you think you know what a mushroom is, you can use Wikipedia or Google to see whether there are matching images. Lots of people do this and lots of people get the wrong answers. Try it with an iconic and easily identifiable fungus like Amanita muscaria. A hansome 85% of the first 100 images that appear on Google areA. muscaria, but 15% are doubtful and if you are a beginner there is no guidance about which is correct. Try a New Zealand Russula or Mycena and the hit rate is a lot lower, below 5 %.
But, things are looking up, websites like PDD’s Virtual Mycota, Clive Shirley’s Hidden Forest and Shirley Kerr’s Kamai Bush all offer reliable images and some guidance.use these rather than Dr. Google or the Blue Swami.
Conclusions
In an ideal world, keys would be constructed to use easily observable characters first and banish the harder questions to last. Common species would be identified first and rare ones last. Websites would be curated by professionals and erroneous information edited out. But, there are no perfect keys or websites that achieve this. This is what field keys set out to try to achieve and why in my view they remain important.
Pat Leonard
28 May 2018
References:
Hidden Forest: http://www.hiddenforest.co.nz/fungi/
Kaimai Bush: https://www.kaimaibush.co.nz/
Kibby, G. (2012) The Genus Russula in Great Britain with synoptic keys to the species.
Knudsen, H andVesterholt, J. Funga Nordica: Agaricoid, Boletoid, Clavarioid, Cyphelloid, and Gastroid Genera, 2nd edition. ISBN 978-87-983961-3-0 (Hardcover, two volumes, 1083 pages).Nordsvamp: Copenhagen, Denmark
May, T.W., Thiele, K., Dunk, C.W. & Lewis, S.H. (2014).FunKey: an Interactive Guide to the Macrofungi of Australia. Key to Agarics.Version 1.Identic, Brisbane & ABRS, Canberra.
MycoKey 4.1 (2014) Asynoptical key to 2000 species of basidiomycetes and ascomycetes in Northern Europe developed by Thomas Lassoe and Jens Petersen
Soop, K. (2017) Cortinariod Fungi of New Zealand.An iconography and Key.Editions Scientrix.karl. soop.org
Virtual Mycota: https://virtualmycota.landcareresearch.co.nz/webforms/vM_Genus_A2Z.aspx
Add new comment