Green Stuff Growing on Tree Bark in Florida: Lichen, Algae, Moss, or Disease?

Green, gray, blue-green, white, orange, leafy, crusty, or fuzzy material on bark is often surface growth rather than something feeding on the tree.

Lichen commonly uses bark as a place to live. Algae and moss favor moisture and shade. Those organisms are different from parasitic algal disease, a fungal conk, a canker, wetwood, or decayed bark.

Do not scrape, pressure-wash, bleach, paint, or spray the trunk before identifying what is present and checking the tree as a whole.

Compare the appearance and the tissue beneath it

Appearance	What it may be	What to check next
Flat crust, leafy patch, or small branching growth in gray, green, white, yellow, or orange	Lichen	Is bark firm and the canopy otherwise normal?
Thin green film or stain on a damp shaded surface	Algae	Is irrigation wetting the trunk? Does the surface dry?
Soft, small, plant-like mat in a persistently damp area	Moss	Is shade, drainage, or repeated trunk wetting present?
Raised or velvety lesions that affect leaves, twigs, or bark tissue on a susceptible host	Parasitic algal disease may be possible	Identify the host and seek plant diagnosis
Shelf, hoof, bracket, or mushroom-like structure attached to trunk or roots	Fungal fruiting body or conk	Assess the associated wood and tree structure
Sunken, dead, cracked, or swollen bark area	Canker or wound response	Check progression, host, dieback, and wood condition
Dark wet streak emerging from a wound or crack	Wetwood, slime flux, or another wound-related condition	Do not drill; evaluate the wound and whole tree
Soft bark, cavity, loose dead tissue, or root-flare decay	Decay rather than harmless surface growth	Keep targets clear and request qualified assessment

A photograph of color alone is not enough. Texture, attachment, host species, tissue damage, canopy condition, and change over time are more useful.

Lichen usually is not the cause of decline

Lichen is a partnership involving a fungus and a photosynthetic partner. Extension guidance explains that lichens generally use bark as a substrate and do not take water or nutrients from the tree’s inner tissues.

That means a healthy tree can carry lichen without needing treatment.

Lichen may become more noticeable when:

• the canopy thins and more light reaches bark,
• growth slows,
• a branch is old or exposed,
• humid air and periodic wetting support surface growth,
• the bark provides a stable attachment area.

Heavy visibility can coincide with stress without causing that stress. Ask why the canopy changed rather than trying to kill the lichen.

Algae and moss point to the surface environment

A green film or mossy patch often reflects a damp microclimate.

Check:

• sprinkler heads striking the trunk,
• dense shade,
• mulch against bark,
• poor air movement,
• a low area that stays wet,
• roof runoff,
• vines covering the trunk,
• soil or fill piled over the root flare.

Correcting unnecessary trunk wetting can be reasonable. Do not expose roots, strip bark, or aggressively thin a mature tree to make the trunk look clean.

Parasitic algae are a separate diagnosis

Some tropical and subtropical hosts can develop algal leaf or stem disease caused by parasitic algae such as Cephaleuros species. UF/IFAS fruit-tree guidance describes algal lesions that can affect leaves and stems and, in some hosts, contribute to bark cankers or twig injury.

This is not the same as a harmless green film or lichen colony.

Seek plant diagnosis when you see:

• discrete raised or velvety lesions,
• spots on leaves and stems as well as bark,
• tissue cracking or swelling beneath the lesion,
• twig dieback,
• a susceptible tropical fruit or ornamental host,
• symptoms that spread rather than remain as a stable surface patch.

Do not choose a copper product or fungicide without identifying the host and disease, checking the label, and confirming that treatment is needed.

A conk is not moss or lichen

Conks and mushrooms are reproductive structures of fungi. Some are associated with dead surface material; others may be connected to internal wood decay.

A conk attached to the trunk, buttress roots, or root flare deserves a different response from lichen.

Photograph:

• shape and size,
• top and underside,
• attachment point,
• nearby cavities or soft wood,
• whole tree and targets.

Read what conks can mean on a tree trunk rather than scraping the structure off and assuming the problem is gone.

Cankers and wet streaks involve bark tissue

A canker is an area where bark and underlying tissue have died. It may be sunken, swollen at the margins, cracked, discolored, or associated with branch dieback.

Wetwood or slime flux may produce dark liquid from a crack or wound. Drilling holes to drain a trunk is not recommended because it creates additional wounds and does not repair the underlying condition.

Use the guide to cracks in tree bark when growth appears alongside an opening, split, or load-bearing defect.

Inspect the whole tree before deciding it is cosmetic

From the ground, check:

• crown density compared with the species,
• new growth,
• dead branches,
• one-sided dieback,
• trunk cracks and cavities,
• bark firmness,
• conks or mushrooms,
• visible root flare,
• soil movement,
• lean,
• construction or trenching history,
• storm change,
• nearby targets.

Surface growth on firm bark with a full, stable canopy is different from surface growth on a declining tree with base decay.

What not to do

Avoid:

• wire brushing,
• pressure washing,
• scraping with a knife,
• bleach or household cleaners,
• random copper or fungicide use,
• painting or sealing bark,
• removing live bark to inspect beneath the growth,
• heavy canopy thinning to reduce shade,
• climbing to collect a sample near dead limbs or utility lines.

Bark protects living tissues. A cosmetic cleaning attempt can create the wound the tree did not have before.

Build a useful identification photo set

Take:

1. the whole tree,
2. the canopy,
3. the trunk from several feet away,
4. a close-up with a scale object beside, not on, the growth,
5. the edge where growth meets normal bark,
6. the root flare,
7. any leaf, twig, or fruit symptoms,
8. any conk, cavity, crack, or wet streak,
9. the irrigation and drainage setting.

A county Extension office or UF/IFAS diagnostic service can help route uncertain plant, fungal, or disease samples.

Choose the appropriate response

Leave it alone

Reasonable when the growth is identified as lichen, algae, or moss; bark remains firm; the crown is normal; and no structural warning signs are present.

Correct the environment

Reasonable when sprinklers, mulch, shade, or drainage are keeping the trunk unnecessarily wet.

Seek plant diagnosis

Appropriate when lesions damage tissue, spread to leaves and twigs, form cankers, or require a pesticide decision.

Request tree assessment

Appropriate when the growth accompanies major deadwood, base decay, cracks, cavities, lean, root movement, or recent storm change.

Scope physical tree work

A defined tree-trimming service may address dead or defective branches. Tree removal is considered when the whole tree’s condition and targets make preservation impractical, not because lichen is visible.

ProTreeTrim can help connect Florida property owners with local providers for tree assessment conversations, trimming, or authorized removal after the organism and structural issue are separated. Call (855) 498-2578.

ProTreeTrim is a referral and dispatch network, not a plant laboratory, fungal-identification service, pesticide applicator, utility, tree-risk assessor, or licensed contractor. Verify diagnosis, labels, credentials, insurance, permits, and scope with the responsible professionals.

Sources and further reading

• Penn State Extension: Do Lichens Cause Harm to Trees?
• Penn State Extension: Lichen in the Garden
• UF/IFAS: Mango Growing in the Florida Home Landscape
• UF/IFAS: Florida Plant Disease Management Guide—Guava
• UF/IFAS: Plant and Pest Diagnosis and Identification Through DDIS
• Penn State Extension: Bacterial Wetwood or Slime Flux