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The characters
used in the key can all be seen with the naked eye or with a x10 hand lens, and are
illustrated in the glossary. However in some places we have included additional characters in the key (and in
the descriptions) that are useful to identify a species. Many lichens contain chemical compounds, some of
which have been used to make dyes, and others as sunscreen products. These compounds are also useful in
identification, and we have included colour reactions for simple spot tests which can help you to identify
some of these species. These spot tests are easy to do in the field and are described below.
Spot tests:
simple spot tests have been used for many years to identify lichen substances that have a colour
reaction. Note that a + denotes a positive colour reaction and a – indicates that there is no colour change. If
you want to use the substances in the field you only need very small amounts (c. 20cc) which can be put in
eye dropper bottles and kept in the fridge when not in use.
Sodium hypochlorite (C)
is common bleach, the thin cheap variety without any additives is the best. Keep
the bottle in the fridge if you want to use it repeatedly over several weeks. Avoid getting it on your clothes.
Potassium hydroxide KOH (K)
or alternatively sodium hydroxide (NaOH - caustic soda) is used as a 10%
solution in water. Care should be taken preparing this as it is highly caustic in the concentrated form. Both
these substances are applied as a small drop to the cortex, or to the medulla after scraping away the cortex.
Record the colour reaction carefully and any change in colour that occurs. On some specimens it is easier to
see the colour reaction by pressing a corner of tissue on the spot where you have made the test and recording
the colour on the tissue.
Paraphenylenediamine (P)
is not readily available except from a lab and is not recommended for use
outside laboratory conditions. It is available as crystals and can be dissolved in alcohol in order to test the
specimen. Alternatively it can be made into a stable solution for regular use called Steiner’s solution.
Instructions are available in most lichen identification books.
KC
This test is used to detect certain compounds to give a pink or red reaction by applying K first and then
C. The reaction may be fleeting, so observe carefully when you apply the C.
UV
Some lichens respond vividly to ultra violet light and the colour may be an important feature for
identifying a species, especially the bright blue-white colour that distinguishes alectoronic acid in several of
the
Parmotrema
species. Battery-operated long wave (365 nm) lamps are widely available now for philatelic
purposes.
Short Glossary
•
Apothecium
(pl. apothecia), a saucer-like fruiting body in which ascospores are produced.
•
Cilia
(single -ium), hair-like outgrowths from the margin of the thallus
•
Cortex
(-icate), outer skin-like layer of the upper or lower surface of the thallus.
•
Isidia
(single = isidium), a corticated outgrowth of the thallus which may be cylindrical, simple, coralloid
or branched..
•
Lobulate
, having small lobes on the thallus or apothecium.
•
Maculate
, spotty or blotchy appearance of the upper surface (visible with or without a x10 lens).
•
Medulla
, the loose area of fungal hyphae below the cortex and the photobiont layer.
•
Photobiont
, a photosynthetic symbiont which in Parmeliaceae is a green alga.
•
Pruina
: (adj. –ose), a frost-like or flour-like surface covering.
•
Pseudocyphella
(pl. pseudocyphellae), dot-like or irregular pale spots on the surface of the thallus where
the medulla is exposed.
•
Pustule
, a blister-like spot that may become sorediate.
•
Rhizine
, a root-like structure on the lower surface of the thallus acting as an attachment organ
•
Soredia
(single –um, adj. -ate), a non-corticate loose weft of hyphae and photobiont cells, granular to
flour-like, produced from pores or cracks on the surface of the thallus, that act as vegetative propagules.
•
Thallus
, the vegetative body of a lichen.