Lichen Identification Guide: Field Key, Look-Alikes & Spot Tests

Is It a Lichen at All?

Several things on bark and rock are regularly mistaken for lichens. Rule them out first:

What you see	Probably	How to tell
Tiny green leaves on stems, soft cushions or carpets	Moss (a plant)	Under a lens you can see individual leaves on a stem. Lichens have no leaves or stems; they are crusts, lobes, cups or branches.
Thin, bright green film or stain on bark, fences or walls, often on the damp side	Free-living green algae	A uniform green coating with no lobes, cups, discs or powdery granules. A lichen crust usually has a definite edge, texture or fruiting bodies.
Orange to rusty film on bark, rock or mortar	*Trentepohlia*, a free-living orange alga	A powdery film with no lobes or discs. Orange lichens such as Xanthoria have lobes or fruiting discs and turn K+ purple.
Soft, pale grey to blue-grey powder on shaded bark or rock overhangs	A dust lichen (Lepraria)	A lichen made entirely of soredia-like granules, with no cortex. Usually paler and greyer than an algal film; L. incana glows blue-white under UV.
Brackets, gills, jelly blobs on dead wood that appear after rain and rot away	A non-lichen fungus	Scratch a lichen and you usually see a thin green layer of algae just under the surface; other fungi have no such layer.

The 8-Step Visual ID Process

Before reaching for reagents or a microscope, careful observation with a hand lens (10x) will take you surprisingly far. Work through these eight steps in order for every specimen.

Step	Observation	Key Questions	Narrows To
1	Growth Form	Crustose, foliose, fruticose, squamulose, gelatinous, or leprose?	Major group
2	Color	Green, gray, yellow, orange, brown, black? Note both wet and dry color.	Order / Family
3	Substrate	On bark (corticolous), rock (saxicolous), soil (terricolous), or wood (lignicolous)?	Ecological group
4	Lobe Shape	Broad or narrow lobes? Rounded or pointed tips? Flat or ascending margins?	Genus
5	Reproduction	Soredia, isidia, apothecia, perithecia, or lobules present?	Species group
6	Underside	Black, white, brown, or tan? Rhizines simple or branched? Veins visible?	Genus / Species
7	Special Features	Cilia, pseudocyphellae, cyphellae, tomentum, pruina, or lirellae?	Species
8	Geography & Habitat	Region, elevation, forest type, microhabitat, exposure?	Confirms ID

Step-by-Step in Detail

Growth Form

This is always your starting point. Is the lichen a flat crust fused to the surface (crustose), a leafy structure you can peel up at the edges (foliose), a three-dimensional shrubby or hanging form (fruticose), overlapping scales (squamulose), a jelly-like mass (gelatinous), or a powdery dusting with no visible structure (leprose)? Growth form alone eliminates the vast majority of possible species.

Crustose

Foliose

Fruticose

Squamulose

Gelatinous

Leprose / Crustose

Color

Record the color carefully, and note whether the specimen is wet or dry, since many lichens change color dramatically with moisture. Dry gray-green lichens often become vivid green when wet. Bright yellows and oranges usually indicate specific chemical compounds (usnic acid, anthraquinones) that narrow identification immediately.

Substrate

What the lichen is growing on matters enormously. Many species are strict specialists: Xanthoria parietina favors nutrient-enriched bark and rock, while Rhizocarpon geographicum grows exclusively on siliceous rock. Note the specific tree species if on bark, and rock type (limestone vs. granite) if saxicolous.

Saxicolous (rock)

Corticolous (bark)

Terricolous (soil)

Lignicolous (wood)

Lobe Shape

For foliose lichens, lobe morphology is critical. Are lobes broad (over 5 mm) or narrow? Are the tips rounded, truncate, or pointed? Do the margins curl up, lie flat, or curl under? Are the lobes tightly appressed to the substrate or loosely ascending? These details separate genera that look superficially similar.

Reproductive Structures

Look for apothecia (open disc-shaped fruiting bodies), perithecia (flask-shaped bodies embedded in the thallus), soredia (powdery granules), isidia (finger-like outgrowths), or lobules (tiny lobe-like propagules). The presence or absence of these structures is one of the most important species-level characters.

Apothecia

Perithecia

Soredia

Isidia

Podetia

Underside Examination

Gently lift a lobe edge to examine the lower surface. Is it black, brown, white, or tan? Are there rhizines (root-like attachment structures), and if so, are they simple, squarrose (brush-like), or dichotomously branched? Some genera have distinctive undersurface features: Peltigera has raised veins, and Sticta has round pores called cyphellae.

Peltigera showing veined underside and rhizines

Rhizines & veins (Peltigera)

Cyphellae (Sticta)

Pseudocyphellae (Punctelia)

Special Features

Look for cilia (hair-like projections from lobe margins), pseudocyphellae (white dots or lines on the upper surface that are pores in the cortex), tomentum (a fuzzy felt-like covering), or pruina (a frosty white coating). These micro-characters often clinch the identification when everything else is ambiguous.

Geography & Habitat

Where you are matters. Many lichens have restricted geographic ranges, and distribution is a valid identification character. Note your region, elevation, forest type (old-growth vs. secondary), aspect (north-facing vs. south-facing), and proximity to pollution sources. A lichen that looks like Lobaria pulmonaria but grows near a highway probably is not — it requires clean air.

Soredia vs. Isidia — The Critical Distinction

Both are asexual reproductive structures, but they differ fundamentally and separating them is one of the most important skills in lichen identification.

Soredia

Powdery granules erupting from breaks in the cortex (called soralia). Loose bundles of algal cells wrapped in fungal hyphae, with no cortex of their own. Look dusty or granular under a hand lens.

Isidia

Finger-like, coral-like, or cylindrical outgrowths from the thallus surface. Crucially, they have their own cortex: a smooth, intact outer layer. Look like tiny organized projections, not like dust.

Many species pairs are separated solely by this character. For example, Parmelia sulcata has soredia in its cracks, while Parmelia saxatilis has isidia. They are otherwise nearly identical.

Field Key: From Growth Form to Genus

Start with the growth form, then follow the colour and substrate to a short list. Each row gives the features you can actually see (or test) and the common lichens that match them in North America and Europe. A photo-based match is usually safe to genus; confirming the species often needs the spot test listed, or a regional guide.

1. Hanging or shrubby (fruticose)

Colour & shape	Where	Check	Likely
Pale yellow-green, round branches	Tree branches	Pull a strand: white elastic central cord	Usnea (old man’s beard); one very long strand with short, even side branches = Dolichousnea longissima
Pale yellow-green, round, stiff hair-like strands	Conifer branches	No central cord	Alectoria
Brown to black hair-like tangles	Conifer branches	No central cord	Bryoria (horsehair lichen)
Flat straps, same colour on both sides, firm	Bark, twigs	No cord; often marginal soralia	Ramalina; lace-like nets in coastal California = R. menziesii
Soft flat straps, green-grey above, white below	Bark, twigs	All spot tests negative	Evernia prunastri (oakmoss)
Grey straps, underside darkening to black, scurfy with isidia	Conifer bark	Cortex K+ yellow	Pseudevernia furfuracea
Brilliant chartreuse-yellow tufts	Conifers and old wood, western North America	Colour alone is distinctive	Letharia vulpina (wolf lichen)
Grey-green or yellowish cups, sticks or red-tipped stalks	Soil, logs, stumps	Hollow stalks rising from small scales	Cladonia: see the cups and sticks table
Grey or yellowish, much-branched mats	Ground in boreal forest, heath, tundra	K and P test	Reindeer lichens: see the reindeer table
Olive to chestnut-brown channelled lobes with spiny edges	Heath, tundra, mountain soil	White pseudocyphellae on the underside	Cetraria islandica (Iceland moss)

2. Leafy, with a separate underside (foliose)

Colour & shape	Where	Check	Likely
Grey with a net of white lines	Bark, rock	Soredia or isidia in the net? Underside black	Parmelia sulcata (soredia) or P. saxatilis (isidia)
Grey with scattered white dots	Bark	Medulla C+ red; underside tan to brown	Punctelia
Yellow-green, broad wrinkled lobes, no white dots	Bark, especially oak	Medulla P+ orange-red, C−	Flavoparmelia caperata (common greenshield)
Yellow-green, tightly attached	Rock	Always on rock	Xanthoparmelia (rock shields)
Grey, broad lobes with black hairs (cilia) on the margins	Bark	Underside black with a bare brown edge	Parmotrema
Grey, puffy hollow lobes, black underside, no rhizines	Twigs, conifer bark	Squeeze a lobe: it is hollow	Hypogymnia physodes
Small pale grey to white rosettes, narrow lobes	Twigs, enriched bark, walls	Cortex K+ yellow	Physcia; see the rosette table
Orange to yellow-orange	Bark, rock, concrete	K+ purple	Xanthoria, Xanthomendoza, Rusavskia
Tiny lemon-yellow lobes under 1 cm	Roadside tree bark	K−	Candelaria concolor
Large lobes, green when wet, with dark “freckles”	Moss and soil	Cephalodia on the upper surface	Peltigera aphthosa
Large grey-brown lobes, veined felty underside	Moss, soil, logs	Raised veins and long rhizines below	Peltigera (dog lichens)
Large green-brown lobes with a network of ridges	Old trees in humid forest	Looks like lung tissue	Lobaria pulmonaria
Leathery, held by one central point	Rock	Single central holdfast (umbilicus)	Umbilicaria (rock tripe)

3. Crust fused to the surface (crustose and leprose)

Colour & shape	Where	Check	Likely
Yellow-green patches outlined in black	Siliceous rock, uplands	Black prothallus between areoles	Rhizocarpon geographicum (map lichen)
Egg-yolk yellow granules	Rock, concrete, posts	K−	Candelariella vitellina
Orange crust or lobed rosette	Rock, walls	K+ purple	Caloplaca and relatives, Rusavskia elegans
Yellow-grey rosettes with lobed edges and crowded discs	Walls, pavements, gravestones	Discs paler than the thallus	Protoparmeliopsis muralis
Grey-white crust with black, script-like lines	Smooth bark	Lirellae	Graphis scripta
Thin white crust like whitewash	Shaded bark	K+ yellow turning red	Phlyctis argena
Matt black band	Seashore rock above high tide	Cracked, with tiny black dots	Hydropunctaria maura (black tar lichen)
Pink balls on short white stalks	Bare acid soil, road cuts	Stalked, round heads	Dibaeis baeomyces
Mint-green crust with flat pink discs	Rotting logs, peat	Discs unstalked	Icmadophila ericetorum
Grey-green crust ringed with red	Bark, southeastern US	Red cottony rim, white band	Herpothallon rubrocinctum (Christmas lichen)
Pale grey to blue-grey powder only	Shaded bark, overhangs	No cortex, no discs	Lepraria (dust lichens)

4. Rubbery or jelly-like when wet (gelatinous)

Dark olive to black, brittle when dry, swelling and translucent within minutes of rain. These are cyanobacterial lichens: Collema has no cortex and becomes thick and pulpy when wet; Leptogium and Scytinium have a cortex one cell thick and are usually thinner and wrinkled. Several small species are now split between these genera, and a microscope section is the reliable test.

Chemical Spot Tests

Many lichen species are visually identical but differ in their secondary chemistry. Five reagent tests (each targeting different compound classes) let you distinguish them in the field. Apply reagents to the cortex or scratch through to the medulla, depending on which layer you need to test.

K Test — Potassium Hydroxide

Apply a small drop of 10% KOH solution to the cortex or exposed medulla. Watch for a color change: K+ yellow indicates atranorin; K+ yellow turning red indicates salazinic acid; K+ orange-brown suggests norstictic acid. K− (no reaction) is equally informative. This is the single most useful spot test and the one to learn first.

C Test — Calcium Hypochlorite (Bleach)

Apply diluted household bleach to the cortex or medulla. C+ pink or red indicates gyrophoric acid or lecanoric acid. Many lichens are C− (no reaction), which is also a useful data point. The C test is especially important for crustose species where K alone is insufficient.

KC Test — Sequential Application

Apply K first, then immediately apply C to the same spot. The combined reaction may differ from either reagent alone. KC+ pink or red-orange detects alectoronic acid and physodic acid, compounds that are invisible to K or C individually. Always record K and C results separately before testing KC.

P Test — Paraphenylenediamine

Apply P reagent to the medulla (scratch through the cortex first). P+ orange or red indicates fumarprotocetraric acid or protocetraric acid. These are among the most common lichen compounds and P is essential for distinguishing many look-alike species.

Safety warning: Paraphenylenediamine is toxic and a known carcinogen. Always wear gloves and avoid skin contact. Work in a well-ventilated area. Many field lichenologists use P dissolved in ethanol and apply it with a fine brush or cotton swab. Dispose of waste properly.

UV Fluorescence — Long-wave 365 nm

Some lichen compounds fluoresce under long-wave ultraviolet light. Blue-white, orange, or yellow fluorescence can indicate divaricatic acid, squamatic acid, and other compounds. UV is non-destructive, requires no reagents, and is especially useful in the field after dark. A portable 365 nm UV flashlight is an inexpensive but powerful addition to any lichen toolkit.

Spot-Test Quick Reference

The reactions you are most likely to see on common species, and what they point to. Results apply to the layer named: scratch through the cortex with a blade to test the white medulla.

Reaction	Layer	Usual cause	Common examples
K+ yellow	Cortex	Atranorin	Physcia, Parmelia, Punctelia, Pseudevernia, Cladonia rangiferina
K+ purple to crimson	Cortex, discs	Anthraquinones (parietin)	Xanthoria, Xanthomendoza, Rusavskia, Caloplaca, Teloschistes
K+ yellow, slowly turning red	Medulla or thallus	Salazinic or norstictic acid	Parmelia sulcata and P. saxatilis (salazinic); Phlyctis argena (norstictic)
C+ red (fleeting)	Medulla	Lecanoric acid (gyrophoric acid gives C+ pink to rose)	Punctelia rudecta, Flavopunctelia
KC+ yellow	Cortex	Usnic acid	Alectoria, Cladonia stellaris
P+ red or orange-red	Medulla, podetia	Fumarprotocetraric or protocetraric acid	Cladonia pyxidata, C. chlorophaea, C. fimbriata, C. rangiferina, Cetraria islandica, Flavoparmelia caperata
UV+ white or blue-white	Thallus	Squamatic, perlatolic and other acids	Lepraria incana, one chemotype of Cladonia squamosa, Icmadophila, some C. stellaris
All negative	–	No reactive compounds	Candelaria concolor, Evernia prunastri, Hydropunctaria maura

Getting reliable results.

Use a tiny drop on a small spot and watch it through a hand lens as it goes on. C and KC reactions can flash and fade within about a second, so look at the moment of application. Some K reactions develop: salazinic acid goes yellow first and turns red over the next few seconds. Household bleach works as C reagent but weakens quickly, so replace it often and keep it in a dark bottle. K (10% potassium hydroxide) is caustic, and P stains skin and is toxic. Always note negative results too, since “K−” is as useful as “K+”.

Thin-Layer Chromatography (TLC)

When spot tests are ambiguous or you need to identify the exact compound present, thin-layer chromatography is the gold standard. TLC separates individual chemical compounds from a lichen sample and compares them to known standards, giving definitive chemical identification.

How TLC Works

A small fragment of lichen is dissolved in acetone or another organic solvent and spotted onto a glass plate coated with silica gel. The plate is placed upright in a developing chamber containing a carefully calibrated solvent system. As the solvent wicks upward by capillary action, different compounds travel at different rates depending on their polarity and molecular weight. The result is a series of separated spots, each representing a single compound.

By comparing the position (Rf value) and color of each spot against known standards run on the same plate, the lichenologist can identify the exact compounds present. This is how the more than 800 known lichen secondary compounds have been catalogued, and it remains the definitive method for chemical identification when spot tests leave doubt.

When to use TLC: TLC is most valuable when two species are morphologically identical and differ only in chemistry, so-called chemical species or chemotypes. It is also essential when publishing new species descriptions, as chemical data is now considered a required component of lichen taxonomy.

Key Look-Alike Pairs

These commonly confused species pairs illustrate why careful observation and chemistry matter. Learning to separate them will sharpen your identification skills across the board.

Parmelia sulcata

Hammered Shield Lichen

Gray-green foliose lichen with a distinctive network of ridges (reticulate pattern) on the upper surface. Soredia develop in the cracks of this network. Look for powdery, granular material filling the grooves. Very common on bark and fences throughout the Northern Hemisphere.

K+ yellow • Soredia in cracks

Parmelia saxatilis

Crudely Wrinkled Shield Lichen

Nearly identical gray-green foliose lichen with the same reticulate upper surface. But instead of soredia, it bears cylindrical isidia: small, cortex-covered outgrowths. Under a hand lens, the surface looks bumpy and organized rather than dusty.

K+ yellow • Isidia (not soredia)

Usnea

Old Man's Beard

Pale green to gray-green hanging fruticose lichen. The diagnostic test: gently stretch a branch. An elastic white central cord will be revealed inside. This is unique to Usnea and present in every species of the genus. Color is typically pale yellowish-green. Contains usnic acid.

Elastic central cord present • Pale green

Bryoria

Horsehair Lichen

Dark brown to black hanging fruticose lichen that superficially resembles dark Usnea. The key difference: no central cord. When you pull a branch apart, it simply snaps or separates into fibers. There is no elastic white strand inside. Generally darker in color than Usnea.

No central cord • Dark brown to black

Cladonia pyxidata with corticate squamules

Cladonia chlorophaea

Mealy Pixie-Cup

Forms small trumpet-shaped cups (podetia) rising from a base of basal squamules. The inside and outside of the cups are covered in fine, granular soredia giving them a mealy, farinose texture. The cups appear powdery and slightly rough under magnification.

Cups sorediate (mealy) • P+ red

Cladonia pyxidata

Pebbled Pixie-Cup

Very similar trumpet-shaped cups, but instead of soredia, the surfaces are covered in corticate squamules: tiny, flattened, scale-like structures with a proper cortex. Under a lens, the cups look rough and scaly rather than powdery. A classic soredia-vs-cortex distinction.

Cups squamulose (scaly) • Corticate

Physcia adscendens

Hooded Rosette Lichen

Small gray-white foliose lichen with ascending lobe tips. The soralia are hood-shaped (helmet-shaped): the lobe tip curls over to form a little hood with soredia produced on the inner, protected surface. Cilia present along lobe margins.

Hood-shaped soralia • Tips curl over

Physcia tenella

Resembles P. adscendens

Very similar gray-white foliose lichen, but the soralia are lip-shaped rather than hooded. The lobe tips bend back slightly to expose soredia on an open, lip-like surface rather than enclosing them in a hood. Cilia also present. Requires a hand lens to separate reliably from P. adscendens.

Lip-shaped soralia • Tips bend back

Ramalina farinacea, same color both sides

Evernia prunastri

Oakmoss

Soft, strap-shaped fruticose lichen with distinct upper and lower surfaces. The upper surface is gray-green while the underside is conspicuously white. This two-toned appearance is the quickest way to recognize Evernia. Used extensively in the perfume industry.

White underside • Two-toned

Ramalina farinacea

Farinose Cartilage Lichen

Also strap-shaped and fruticose, but the same color on both sides: a pale yellowish-green throughout. No distinct upper/lower differentiation. Often bears marginal or laminal soredia along the branches. Firmer and more cartilaginous than the soft straps of Evernia.

Same color both sides • Uniform

Look-Alike Comparison Tables

The groups that cause the most confusion, side by side. Read across a row for the features that separate each lichen from its neighbours. Each feature is something you can see with a 10× lens or check with a single spot test.

Beards and straps: Usnea vs Ramalina vs Evernia and relatives

Lichen	Branches	Colour	Inside / underside	Other clues
Usnea	Round in section	Pale yellow-green to grey-green; some species reddish	White elastic central cord	Often with soredia, isidia or tiny side spines; cortex usnic acid
Dolichousnea longissima	One very long axis with short, even side branches	Pale yellow-green	Central cord	Strands to several metres; humid old forest
Ramalina	Flat or angular straps (a few species round)	Same pale yellowish-green on both sides	No cord; firm, cartilaginous	Soralia on margins or surface in sorediate species
Evernia prunastri	Soft, flat, forking straps	Green-grey above	White underside, no cord	Soralia start as discrete spots on ridges and margins; all spot tests negative
Evernia mesomorpha	Angular, flabby, ridged	Pale yellow-green all round	No white underside	Coarse soredia on the ridges
Pseudevernia furfuracea	Flat straps forking in one plane	Grey above	Underside white to pinkish when young, blackening with age	Isidia; no rhizines; cortex K+ yellow
Alectoria sarmentosa	Round, hair-like, stiff	Pale yellowish-green; tips may blacken	No cord	White pseudocyphellae on the branches; cortex KC+ yellow
Bryoria	Round, hair-like	Brown to black	No cord	Never KC+ yellow

Grey and green shields: Parmelia vs Punctelia vs Flavoparmelia

Lichen	Colour	White markings	Propagules	Underside	Spot test
Parmelia sulcata	Grey to blue-grey	Net of white lines (reticulate pseudocyphellae)	Soredia in the net	Black, rhizines simple to bottle-brush	Medulla K+ yellow→red
Parmelia saxatilis	Grey, browner tips	Net of white lines	Isidia, no soredia	Black, rhizines simple	Medulla K+ yellow-orange→red
Punctelia rudecta	Grey to blue-grey	Scattered white dots	Isidia	Pale tan to brown	Medulla C+ red
Punctelia subrudecta group	Grey	White dots	Soredia	Pale brown	Medulla C+ red
Flavoparmelia caperata	Pale yellow-green	None	Coarse granular soredia in pustules	Black, brown at the edge	Medulla P+ orange-red, C−
Flavopunctelia	Yellow-green	White dots (minute in F. soredica)	Soredia	–	Medulla C+ red
Parmotrema	Grey	Usually none	Soredia on lobe edges	Black with a bare brown margin	Lobes broad, often with black cilia

Small rosettes on twigs and walls: Physcia vs Xanthoria and other K-test groups

These often grow together on nutrient-rich bark. One drop of K sorts most of them: grey ones that turn yellow are Physcia; orange ones that turn purple are Xanthoria and relatives; yellow ones that do nothing are Candelaria or Candelariella.

Lichen	Colour	Lobes & features	Underside	K test
Physcia (e.g. P. adscendens, P. tenella)	Pale grey to white	Narrow lobes; hooded (adscendens) or lip-shaped (tenella) soralia; marginal cilia	Pale	Cortex K+ yellow
Physcia stellaris	Pale grey	Star-shaped rosettes, no soredia, many black-disced apothecia	Pale	Cortex K+ yellow
Phaeophyscia	Grey-brown to dark grey	Small lobes, never frosted	Usually black; rhizines black with white tips	K−
Physconia	Grey-brown	Lobe tips often frosted white (pruinose)	Black bottle-brush rhizines forming a fringe	K−
Xanthoria parietina	Orange to yellow-orange; grey-green in deep shade	Broad, flat lobes; abundant orange discs	Pale, with few rhizines	K+ purple
Xanthomendoza fallax	Orange-yellow	Small rosettes with hood-shaped soralia; discs rare	Pale	K+ purple
Rusavskia elegans	Intense orange-red	Narrow, convex lobes, tightly attached; on rock	Pale	K+ purple
Candelaria concolor	Lemon-yellow	Tiny (0.2–0.5 mm) granular-edged lobes, rosettes under 1 cm	White, with white rhizines	K−
Candelariella vitellina	Egg-yolk yellow	Granular crust, no lobes, frequent yellow discs	None (crust)	K−

Cladonia cups and sticks

All of these rise from a base of small leafy squamules. Most are P+ red, so the decisive features are the shape of the stalk and the texture of its surface under a lens: powdery soredia, coarse corticate granules, or a smooth cortex.

Lichen	Shape	Surface	Tips	Notes
C. pyxidata	Wide goblet cups	Coarse, pebble-like corticate granules and scales; no powder	Brown discs or pycnidia on rims	P+ red
C. chlorophaea	Goblet cups tapering gradually into the stalk	Mealy to granular soredia inside and outside the cup	Brown pycnidia on rims	P+ red; worn specimens can match C. pyxidata
C. fimbriata	Narrow trumpet cups set abruptly on a long, slender stalk	Fine, flour-like soredia all over	–	P+ orange-red
C. coniocraea	Pointed horns, no cups (rarely tiny ones)	Powdery soredia above a corticate base	Pointed	Very common on stumps and tree bases
C. cristatella	Unbranched or sparingly branched stalks, no cups	Corticate, often with small scales; no soredia	Bright red apothecia	“British soldiers”; eastern North America
C. macilenta	Slender stalks, no cups	Powdery soredia	Red apothecia	K+ yellow (thamnolic acid)
C. pleurota	Cups	Yellowish-green with coarse granular soredia	Red pycnidia or discs on cup rims	Yellow tint from usnic acid

Reindeer lichens

Lichen	Colour	Branching	Spot tests
C. rangiferina	Silver-grey; dull, woolly surface	Tree-like with a main stem; branches mostly in fours; brownish tips swept to one side	K+ yellow, P+ red
C. stellaris	Pale yellowish-green	Dense rounded “cauliflower” heads, no main stem; tips in fours and fives, star-like	K−, P−, KC+ yellow
C. arbuscula	Yellowish-green	Main stem; tips bent strongly to one side	K−, P+ red
C. mitis	Yellowish-green	Similar to C. arbuscula	K−, P−
C. portentosa (Europe)	Greenish-grey	Distinct main axis; tips mostly in threes; holes in the branch axils	K−, P−

Pink and red fruiting bodies

Lichen	Fruiting bodies	Thallus	Where
Dibaeis baeomyces	Round bubblegum-pink heads on 2–6 mm white stalks	Pale grey warty crust	Bare acid soil, road cuts
Baeomyces rufus	Flattened pink-brown to red-brown caps on short stalks	Grey-green granular crust	Soil and stone
Icmadophila ericetorum	Flat, unstalked pale pink discs	Mint-green crust	Rotting logs, peat
Cladonia cristatella	Scarlet tips on 1–3 cm stalks	Grey-green squamules	Logs, stumps, soil
Herpothallon rubrocinctum	None; the red is a cottony rim and granules	Grey-green crust with white and red zones	Bark, southeastern US

Black patches on rock

What	Look	Where
Hydropunctaria maura	Flat matt black crust, finely cracked like dried mud, with minute black dots (perithecia); hard to remove	Continuous band on shore rock at and above high water
Lichina	Tiny black tufts or cushions, not a flat crust	Just above or below the black crust band
Collema and other gelatinous lichens	Brittle black lobes when dry, swelling to olive jelly when wet	Damp rock, mortar, bark
Oil or tar	No cracked texture or fruiting dots under a lens	Irregular, often at the strandline

Lichen Identification Guide

Why Identification Matters

On This Page

Is It a Lichen at All?

The 8-Step Visual ID Process

Step-by-Step in Detail

Growth Form

Color

Substrate

Lobe Shape

Reproductive Structures

Underside Examination

Special Features

Geography & Habitat

Soredia

Isidia

Field Key: From Growth Form to Genus

1. Hanging or shrubby (fruticose)

2. Leafy, with a separate underside (foliose)

3. Crust fused to the surface (crustose and leprose)

4. Rubbery or jelly-like when wet (gelatinous)

Chemical Spot Tests

K Test — Potassium Hydroxide

C Test — Calcium Hypochlorite (Bleach)

KC Test — Sequential Application

P Test — Paraphenylenediamine

UV Fluorescence — Long-wave 365 nm

Spot-Test Quick Reference

Thin-Layer Chromatography (TLC)

How TLC Works

Key Look-Alike Pairs

Parmelia sulcata

Parmelia saxatilis

Usnea

Bryoria

Cladonia chlorophaea

Cladonia pyxidata

Physcia adscendens

Physcia tenella

Evernia prunastri

Ramalina farinacea

Look-Alike Comparison Tables

Beards and straps: Usnea vs Ramalina vs Evernia and relatives

Grey and green shields: Parmelia vs Punctelia vs Flavoparmelia

Small rosettes on twigs and walls: Physcia vs Xanthoria and other K-test groups

Cladonia cups and sticks

Reindeer lichens

Pink and red fruiting bodies

Black patches on rock

Photographing a Lichen for Identification

Glossary of Terms