The twins Castor and Pollux wear a superficially similar round cap called the pileus.
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A pileus is characteristic of agarics, boletes, some polypores, tooth fungi, and some ascomycetes.
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The most familiar pileus shape is hemispherical or convex.
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A cap-like pileus cloud is visible atop the rising column.
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It was originally to be crowned with a pileus, the cap given to emancipated slaves in ancient Rome.
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The pileus competed with the Phrygian cap, a similar cap that covered the ears and the nape of the neck, for popularity.
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The Phrygian cap eventually supplanted the pileus and usurped its symbolism, becoming synonymous with republican liberty.
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Many well-known species have a convex pileus, including the button mushroom, various Amanita species and boletes.
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In these cases the pileus is termed infundibuliform.
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More examples
Cap: a fruiting structure resembling an umbrella or a cone that forms the top of a stalked fleshy fungus such as a mushroom
The pileus (Greek u03C0u1FD6u03BBu03BFu03C2 - pilos, also pilleus or pilleum in Latin) was a brimless, felt cap worn in Ancient Greece and surrounding regions, later also introduced in Ancient Rome. The Greek u03C0u03B9u03BBu03AFu03B4u03B9u03BFu03BD (pilidion) and Latin pilleolus were smaller versions, similar to a skullcap.
A pileus (Latin for cap), also called scarf cloud or cap cloud, is a small, horizontal cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance. Pilei tend to change shape rapidly. ...
The pileus is the technical name for the cap, or cap-like part, of a basidiocarp or ascocarp (fungal fruiting body) that supports a spore-bearing surface, the hymenium. The hymenium (hymenophore) may consist of lamellae, tubes, or teeth, on the underside of the pileus. ...
The hymenium-bearing structure in non-resupinate basidiomata. pl. pilei. adj. pileate.
The spore-bearing cap or head of a mushroom or other large fungal fructification.
The expanded caplike portion of some basidiocarps or ascocarps that supports the hymenium. (Pl. pilei.) (15)