Cystidium

A cystidium (plural: cystidia) is a relatively large, sterile (non-reproductive) cell found on the hymenium of certain fungi, particularly basidiomycetes. Cystidia are typically microscopic structures, and their presence, shape, size, and ornamentation are important characteristics used in the identification of many fungal species.

Cystidia are not directly involved in spore production. Their exact function is not fully understood, but several hypotheses exist. These include:

• Maintaining humidity: Cystidia may help create and maintain a humid microclimate around the basidia (spore-bearing cells), which is crucial for proper spore development and discharge.

• Physical spacing: Cystidia might serve to physically separate the basidia, preventing them from collapsing together and ensuring proper spore dispersal.

• Defense: Some cystidia may contain chemicals that deter grazing by small animals or inhibit the growth of competing microorganisms.

• Structural support: Cystidia could provide structural support to the hymenium.

Cystidia are classified based on their location, shape, and ornamentation. Common types include:

• Gloeocystidia: Cystidia with oily or refractive contents.
• Lamprocystidia: Thick-walled, encrusted cystidia.
• Metuloids: Thick-walled cystidia, often encrusted.
• Pleurocystidia: Cystidia found on the face of a gill or pore.
• Cheilocystidia: Cystidia found on the edge of a gill or pore.
• Dermatocystidia: Cystidia found on the surface of the cap or stipe.

The observation of cystidia usually requires microscopic examination of a thin section of the fungal hymenium. Different stains and mounting techniques can be used to highlight their features.