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Currently under development. This does not aim to be a comprehensive glossary, but rather an explanation of some common terms used in lichenology and those used on this website. For detailed, English-language glossaries, go (e.g.) to Brodo, Sharnoff, & Shjarnoff, S. (2001), Dobson (2011) or Smith et al. (2009).


 
gyrose
 
Term applied to an apothecium with a contorted surface resulting from multiple infoldings of the margin.
 

gyrose apothecia of Umbilicaria cylindrica
 
hymenium
 
(plural: hymenia)  The tissue in fungal sexual fruiting bodies that (in lichens) produces ascospores or basidiospores. In ascocarps it is primarily composed of asci and paraphyses; in basidiocarps it is primarily composed of basidia.
 
 
 
hypha
 
(plural: hyphae)  A single fungal filament. The mycelium and fungal fruit-bodies are composed of aggregations of hyphae, or largely so.
 
 
 
involucrellum
 
(plural: involucrella)  A usually black, hardened layer of tissue forming a shield-like structure over or enclosing the upper part of a perithecium, but not blocking the ostiole. Microscopic examination of a section down through the perithecium is usually necessary to confirm the presence of an involucrellum; it often cannot be detected by viewing from above. Useful diagrams are provided by Orange (2013, especially section 1.2.1.).
 
 
 
isidium
 
(plural: isidia) (adjective: isidiate)  An asexual propagule enclosed in a cortex, containing fungal tissue and the phycobiont. Isidia are budded off from the thallus cortex and are variously peg-shaped, cylindrical, coral-like or spherical.
 
Isidia are more fully described here.
 

Isidia on the thallus surface in Parmelia saxatilis.
 
K
 
As used in lichenology, 'K' is short-hand for an approx. 10% w/v solution of potassium hydroxide (KOH). A small drop of KOH is placed on the lichen and any colour change noted. Commonly there is no reaction (K-) or alternatively there may be production of a yellow to red or purple colour (K+), specific for the species concerned. It is important to note the tissue that must be tested for a given species, which may be apothecia, the cortex or the medulla. In Cladonia, a red-fruited species may be K- on the thallus and lower part of the podetia, but K+ if any of the reagent reaches the apothecia, or the undersides of the squamules.
KOH for field tests must be carried safely, usually in a small plastic dropping bottle within a rigid container, and the test must be applied with due care, bearing in mind it is caustic.
The solution becomes degraded and must be replaced when it becomes cloudy and begins to lose activity. Dobson (2011) gives more details of 'K' testng. Sodium hydroxide (NaOH) is easier to obtain and is sometimes used as a substitute, but it is said to give a positive crimson reaction with Candelariella species, making it unsuitable for the commonly used chemical separation of Candelariella and Caloplaca. Note also that KOH on a thallus commonly brings out the colour of the algal cells beneath and appears greenish-yellow. It is best to soak some of the drop onto white filter paper to see the colour resulting from the test.
 

Positive (K+ purple) reaction on the thallus of Xanthoria parietina.
 
lichenicolous
 
Inhabiting lichens, i.e. growing on or in lichens, often but not necessarily as parasites (see lichenicolous fungi).
 
 
 
lignicolous
 
Growing on wood from which bark has been stripped, or on worked wood. (Compare corticolous.)
 
 
 
lignum
 
Dead wood, including worked wood.
 
 
 
limestone
 
Sedimentary rock type composed mainly of calcium carbonate and often supporting distinctive lichen communities. Limestones were laid down at various times in the Earth's history and differ in structure and hardness. Limestone gravestones in churchyards often carry a diversity of lichen species.
 

Limestone cliffs at Inchnadamph, W.Sutherland
 
medulla
 
The interior tissue of the lichen thallus, below the upper cortex. Generally the medulla shows little differentiation but the uppermost region commonly contains algal cells and constitutes the photobiontic layer. The tissue is most often white, but may be coloured, e.g. pale yellow in Hypotrachyna endochlora, or pink in Usnea ceratina. Responses to chemical and UV tests may differ from those of the cortex.
 

lobes of Hypotrachyna endochlora, showing damage to the cortex and exposure of the pale yellow medulla beneath
 
mycelium
 
(plural: mycelia)  The non-reproductive ("vegetative") part of a fungus, composed of aggregations of hyphae, or largely so. Generally for substrate decomposition and nutrient absorption.
 
 
 
mycobiont
 
The fungal component of a lichen.
 
 
 
mycota
 
A collective term for fungal species, often of a given locality, region or habitat, the equivalent of 'fauna' (animals) and 'flora' (plants). As fungi are no longer regarded as plants, it is more correct to use the phrase 'lichen mycota' than 'lichen flora', though old habits die hard.
 
 
 
oribatid mite
 
Mite in the large order Oribatida, otherwise known as "beetle mites" (presumably from their toughness and shiny appearance) or "moss mites". They exist mainly in soil, on rotting wood, in mosses and in lichens, feeding on organic and plant debris, including grazing on lichens. Generally their effects on lichens are inconspicuous (see here for an exception) and they remain hidden in/under the lichen for much of the day, but they can be destructive when included in a collected lichen packet. They are resilient, surviving in dry packets for weeks or for months, continuing to graze the lichen, especially destroying apothecia, and also quickly consume the conidia of Illosporiopsis. Modern health and safety practice precludes the use of toxic chemicals and current preference is to place packets of dried lichens in a freezer for several days.
 

oribatid mites on Parmelia saxatilis
 
ostiole
 
As applies to lichens, the apical pore, through which spores are released, of a perithecium or pycnidium.
 
 


 

References
    •   
Brodo, I.M., Sharnoff, S.D., & Shjarnoff, S., (2001). Lichens of North America, Yale University Press, New Haven.
          
    •   
Dobson, F.S. (2011). Lichens. An illustrated guide to the British and Irish species, ed. 6, Richmond Publishing Co., Slough.
          
    •   
Orange A. (2013). British and other pyrenocarpous lichens, ed 2, National Museum of Wales. [Online: available http://www.museumwales.ac.uk/media/13849/Orange,-A.-(2013)-British-and-other-pyrenocarpous-lichens.pdf].
          
    •   
Smith, C.W., Aptroot, A., Coppins, B.J., Fletcher, A., Gilbert, O.L., James, P.W., & Wolseley, P.A. (eds.) (2009). The lichens of Great Britain and Ireland, British Lichen Society, London.
          


 

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Photographs, unattributed line illustrations, scan manipulations of out of copyright sources, and text © A.J. Silverside.
Uploaded January 2013, last modified or updated April 2014.