Definition

Noun 1. The cap of a mushroom or other fungus: The pileus is the umbrella- or cone-shaped, often fleshy, top part of a fungus that bears the spore-producing surfaces (gills, pores, or teeth) on its underside.

Usage

The term pileus is a specialized, scientific term used primarily in mycology (the study of fungi). It is the formal name for the structure commonly called the "cap" of a mushroom or toadstool. It describes the shape, texture, and features of this specific part of the fungal fruiting body.

Examples

• The pileus of this species is convex when young but becomes flat with age.
• Mycologists carefully examine the color and texture of the pileus to help identify the fungus.
• The gills are located on the underside of the mushroom's pileus.

Advanced Usage

• Pileus shape: Descriptors for the shape of the cap are often used in identification keys. Common shapes include convex, flat, umbonate (with a central bump), depressed, or conical.
• Pileus surface: The texture of the cap surface can be described as smooth, scaly, fibrillose, sticky, or dry.

Variants and Related Words

• Cap (n): The common, non-technical synonym for pileus.
• Pileate (adj): Having a pileus or cap-shaped structure.
• Stipe (n): The stalk or stem that supports the pileus.

Synonyms

• Cap
• Mushroom cap

Notes

• Pileus is a singular noun. The standard plural form is pilei (pronounced /ˈpɪliˌaɪ/ or /ˈpaɪliˌaɪ/), though pileuses is also occasionally used.
• This word is almost exclusively used in biological and scientific contexts. In everyday conversation, "cap" is always used instead.

Noun

1. a fruiting structure resembling an umbrella or a cone that forms the top of a stalked fleshy fungus such as a mushroom