Jack-o'-Lantern Mushroom

Toxic

Scientific name	Omphalotus olearius
Family	Omphalotaceae
Portuguese name	Cogumelo-da-oliveira
English name	Jack-o'-lantern mushroom
Season	July, August, September, October
Habitat	Oak forest, Cork oak
Look-alikes	Chanterelle

Description

Omphalotus olearius (jack-o’-lantern mushroom) is a large, brightly orange poisonous mushroom that grows in clusters on dead wood. It possesses a unique ability — bioluminescence: its gills glow greenish in complete darkness. Native to the Mediterranean basin and widespread in Portugal.

Cap

• Diameter: 5–15 cm
• Shape: convex when young, later funnel-shaped (depressed in the centre)
• Colour: bright orange, pumpkin-orange. Uniformly intense colour inside and out
• Surface: smooth, slightly fibrous
• Margin: inrolled, wavy

Stem

• Height: 5–15 cm
• Width: 1–2.5 cm
• Colour: same colour as the cap (orange)
• Ring: absent
• Surface: smooth, often curved
• Base: tapering downwards, attached to wood

Flesh

• Colour: orange-yellow
• Smell: unpleasant, sweetish
• Taste: do not taste!

Spore print

Creamy-yellow.

Bioluminescence

A unique feature of Omphalotus olearius is its glowing gills in complete darkness. The greenish glow is caused by the enzymatic oxidation of luciferin by fungal luciferase. The glow is faint and only visible after prolonged adaptation to complete darkness (at least 10–15 minutes).

Toxicity

Toxin

• Illudin S (sesquiterpene) — the primary toxin. Alkylates DNA, damages rapidly dividing cells
• Muscarine was previously cited, but illudin S is responsible for the toxic effects

Mechanism: illudin S reacts with DNA, creating lesions that block transcription. Genotoxic — induces gene mutations.

Poisoning symptoms

Manifestations:

• Severe abdominal cramps
• Intense nausea and vomiting
• Pronounced diarrhoea
• Weakness, dizziness, sweating
• Dehydration

Fatality: extremely rare. Recovery is usually complete, but the process can be agonisingly prolonged (up to several days).

Where and when

Season

• Main season: July–October (earlier than many other species)
• Characteristic of the Mediterranean climate

Habitats in Portugal

• Oak forests — on dead roots and stumps of holm oak and cork oak
• Olive groves — on dead olive wood (hence the name olearius)
• Grows in clusters on dead wood and buried roots
• Native to the Mediterranean basin
• Documented in Portugal on Wilder.pt and BioDiversity4All

Ecology

Saprotroph — decomposes dead wood. Unlike the chanterelle, which is a mycorrhizal fungus.

Look-alikes

Comparison with the chanterelle

Safety rule

If you find a “chanterelle” growing in a cluster on a stump or dead root — it is NOT a chanterelle. True chanterelles always grow on soil.

See Also

Habitats:

• Montado (Cork Oak Woodlands)

Related articles:

• Safety Rules
• Deadly Species

Sources

1. Kirchmair M. et al. — Toxicology and detoxification of illudin S // Toxicon, 2003
2. Wilder.pt — Que espécie é esta: Omphalotus olearius
3. BioDiversity4All / GBIF Portugal — species records
4. First-Nature — Omphalotus olearius identification
5. La Casa de las Setas — Olive mushroom
6. Sociedade Portuguesa de Micologia

Disclaimer: Identifying mushrooms from descriptions and photographs on the internet is not a substitute for consulting an experienced mycologist. The authors assume no responsibility for the consequences of collecting and consuming mushrooms.