Outline of lichens

Lichen – composite organism made up of multiple species – a fungal partner, one or more photosynthetic partners, which can be either green algae or cyanobacteria, and, in at least 52 genera of lichens, a yeast.

[34][35] Lichens fall into eight fungal classes and several subclasses:[38] They are split across nearly 40 orders.

These were listed in Lücking, Hodkinson and Leavitt's 2016 treatise on the classification of lichenized fungi, except where otherwise noted;[35] families were updated in 2021.

These were listed in Lücking, Hodkinson and Leavitt's 2016 treatise on the classification of lichenized fungi, except where otherwise noted.

[35] In 2009, taxonomists estimated that the total number of lichen species (including those yet undiscovered) might be as high as 28,000.

An intricately branched, pale green lichen hangs from a branch.
Usnea filipendula – one of about 20,000 described species of lichen
Section labeled "a" is grey, dotted with hundreds of small white circles. Section labeled "b" has grey strands surrounding numerous green circles. Section labeled "c" has loosely tangled grey strands with much open space between them. Section labeled "d" mirrors section labeled "a". In the section labeled "e", the structure in section "d" descends to two points - again grey with many white circles
Schematic cross section of foliose lichen :
(a) The cortex is the outer layer of tightly woven fungal filaments ( hyphae )
(b) This photobiont layer has photosynthesizing green algae
(c) Loosely packed hyphae in the medulla
(d) A tightly woven lower cortex
(e) Anchoring hyphae called rhizines , where the fungus attaches to the substrate
A leafy, dark bronze lichen with wavy, white-tipped edges on a piece of bark
Lichens with a cyanobacteria as the photosynthetic partner, like this Peltigera collina , can fix nitrogen . [ 26 ]
Several small brown balls rest atop black stalks rising from a bit of wood.
Chaenotheca brunneola falls into Coniocybomycetes , a small fungal class which contains only a handful of lichen species. [ 34 ]
A thick branch covered with a white crust, marked by black spots and thin black lines.
Lecidella elaeochroma is a member of Lecanorales , the fungal order which contains the greatest number of lichen species. [ 38 ]
Stick covered with flat, yellowy-green, wavy-edged lichen speckled with raised orange spots
Xanthoria parietina has the leafy-looking growth of a foliose lichen . [ 102 ]
Photo of stony ground with one large rock covered in a multitude of lichens of different sizes, shapes and colours
Saxicolous lichens are those which grow on stone. [ 111 ]
Photo of sandy ground with patches of flat brown and bright orange ball-shaped lichens
Namibia 's vast deserts, which hold many species of lichen, remain largely unsurveyed. [ 117 ]
Picture through microscope of four algal cells: round with clear edges and bright green centres
The photobiont in most lichens is a green alga , particularly those from the genus Trebouxia . [ 6 ]
Four photos showing a leafy dark green lichen; the top two are virtually identical, though one photo is labeled C (calcium hypochlorite or sodium hypochlorite) and K (potassium hydroxide) and the other labeled C and KC (K followed immediately by C). The bottom two show a colour change; where the medulla has been exposed, its colour changes to pinkish-red when exposed to C and KC.
Chemical spot tests on the foliose lichen Punctelia borreri showing thallus (top) and medulla (bottom). The pinkish-red colour change of the medulla in the C and KC tests indicate the presence of gyrophoric acid , a chemical feature that helps to distinguish this lichen from similar species in the same genus. [ 121 ]
Two black loaves sit on a plate with knife and fork beside them.
Two baked loaves of Bryoria fremontii , an important traditional food for some First Nations people [ 131 ]