Honey fungus.

Armillaria

Pronounced ar-mil-LAIR-ee-uh

Also known as Armillaria root disease, Honeyfungus, Shoestring root rot, honey fungi, honey mushrooms

Armillaria mellea — Photo by Anisha Kumra (CC BY) via iNaturalist

Armillaria is a genus of parasitic fungi that grow on trees and woody shrubs. These fungi are well known for their bioluminescent properties and their role in forest ecosystems. You will often see them appearing as clusters of mushrooms around the base of infected plants.

At a glance

Care level: Difficult
Plant type: Fungi
Light: Shade
Indoor light: Low light
Water: Every 1 to 7 days
Mature size: Variable
Growth rate: Fast
Hardiness: USDA 3 to 9

Care

This is a parasitic fungus that typically kills its host plant, so it is usually managed as a pathogen rather than a houseplant. Keep an eye out for white fungal mats under the bark or black rhizomorphs in the soil. If you find this in your garden, you should remove the infected plant and its root system entirely.

Watering: They prefer consistently moist environments to thrive.
Feeding: Do not fertilize as this is a parasitic fungus.
Pruning: Remove infected host plant material as needed.
Repotting: Repotting is not applicable for this organism.
Soil: Decaying wood or soil with organic matter
Soil pH: 5.0 to 7.0
Temperature: 0 to 30°C
Humidity: 60 to 95%

Safety

People: Raw specimens are toxic and can cause significant digestive upset.
Pets: Some species are considered edible for humans when cooked, but they are generally not recommended for pets and can cause digestive upset.
Children: Keep children away from wild mushrooms to prevent accidental ingestion of toxic lookalikes.
Contact allergens: Touching the mycelium or fruiting bodies is generally safe, but some people may experience mild skin irritation.
Airborne allergens: Spore release in large quantities can irritate sensitive airways.
Edibility: Many species are edible when cooked thoroughly, but they can cause severe gastric distress if undercooked or if the individual is sensitive.

How to identify it

Clusters of honey colored mushrooms
White spore print
Ring present on the stalk
Black shoestring like rhizomorphs underground

Height: 0.05 to 0.15m
Spread: 0.05 to 0.2m
Leaves: deciduous
Flowers: 0cm
Fruit: honey, brown, Autumn

Problems to watch for

Root RotCommon
Stem RotCommon
Fungus GnatsUncommon
PhytophthoraUncommon

By symptom

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Growing it

Propagation: spores, rhizomorphs

Avoid planting susceptible trees in areas where this fungus is already present in the soil.

Keep away from

Oak — Armillaria is a primary pathogen that causes root rot and death in oak trees.
Pine — Conifers are highly susceptible to infection by Armillaria rhizomorphs.
Apple — Fruit trees are frequently killed by Armillaria root rot in infested soil.

Similar species

Galerina — This deadly mushroom can be mistaken for Armillaria by inexperienced foragers.

Science

Family: Physalacriaceae
Genus: Armillaria
Order: Agaricales
Class: Agaricomycetes
Native range: Widespread across temperate and boreal forests globally.
Conservation: Not of conservation concern as it is a widespread and aggressive pathogen.

It survives by breaking down woody tissue and acting as a primary decomposer in forest ecosystems.

Value to wildlife: decomposer
Uses: culinary, ecological research

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 0/9
Soil reaction: 5/9
Light: 0/9
Temperature: 4/9
Moisture: 7/9
Nutrients: 5/9

Taxonomy resolved against GBIF.

Questions people ask

Is it safe to eat?: Only if identified correctly by an expert and cooked very thoroughly.
Does it kill trees?: Yes, it is a parasitic fungus that causes root rot in many woody plants.

Where the name comes from

The name Armillaria comes from the Latin word armilla, meaning bracelet, referring to the ring on the mushroom stalk.

Good to know

It is commonly known as the honey mushroom.
The fungus spreads through underground root-like structures called rhizomorphs.
It is a major pathogen of trees and woody shrubs.
The bioluminescent mycelium can cause wood to glow in the dark.

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This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.