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cystidium

(pl. cystidia)

Terms discussed: caulocystidium (pl. caulocystidia), cheilocystidium (pl. cheilocystidia), chrysocystidium (pl. chrysocystidia), pileocystidium (pl. pileocystidia), pleurocystidium (pl. pleurocystidia)


See Also:
hymenium
End Cell




Image of Panaeolus semiovatus from Joseph Henri Léveillé (1837) Sur le hymenium des champignons in Annales des Sciences Naturelles. Botanique
Panaeolus semiovatus
A cystidium is a big, funny-looking end cell that sticks out of a gill surface but doesn't look like a basidium. In this image, you see a gill surface formed of a palisade of end cells, the rounded basidia sticking out with their "crown"s of spores, and then the cystidia, even bigger than the basidia, bluntly pointed. Since cystidia have so many shapes, and these shapes hold (fairly) constant for a given species, they are useful in identifying mushrooms.

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Image of Inocybe from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Inocybe
Cystidia have more specific names depending on where they are found on the fruiting body. The default location for a cystidium is in the hymenophore, on the face of a gill or the inside of a tube or pore. Cystidia on the pileus surface are called pileocystidia. On the stalk, they are called caulocystidia, and on the edge of the gill (or tube end) they are called cheilocystidia.

Here, the gill is laying sideways, so the edge of the gill, with its cluster of cheilocystidia, is to the left.

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Image of Plutaceae from Christian Gottfried Daniel Nees von Esenbeck (1816 - 1817) Das System der Pilze und Schwämme
Plutaceae
Distinctive cystidia have been used to identify mushrooms ever since they were first discovered. Here, the distinctive "crowned bottle" cystidia shown in the previous picture are depicted as a characteristic feature of the Plutaceae, in 1817.

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Image of Boletaceae from A. M. Hussey (1847 - 1855) Illustrations of British mycology
Boletaceae

Sometimes the cheilocystidia are strongly colored, and make the edge of the gill or mouth of the pore differently colored from the rest of the gill or tube, and their presence makes the gill edge seem fuzzy or finely fringed, even though they can't be clearly seen individually. The brightly colored pore surface of the red- and yellow-pored boletes is due to their cheilocystidia: the rest of the pore tube is not colored the same way. In fact, some cystidia are specifically named after their golden appearance under the microscope: these are called chrysocystidia. You can see an example of dark-colored gills colored white at the edges by cystidia at http://www.cx.sakura.ne.jp/~kinoko/01eng/psathyrella_bipellis2.htm

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So, you now have two possible ways to detect cheilocystidia without a microscope: they are sometimes differently colored than the face of the gill, and they are sometimes large enough to make the gill margin look finely fringed (use a hand lens!). There is a third method: the cheilocystidia serve an excretory function, so the margin of gills with abundant cheilocystidia are often beaded with tiny droplets of liquid.

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Image of Coprinus micaceus from Joseph Henri Léveillé (1837) Sur le hymenium des champignons in Annales des Sciences Naturelles. Botanique
Coprinus micaceus
I lied before, when I said that cystidia look different from the basidia. Sometimes the cystidia can be roughly the same shape as the basidia, and then there is usually some controversy over whether to call them cystidia or basidioles or paraphyses, or whatever. However, even if the cystidia are roughly the same shape as the basidia, they are usually much bigger and that settles the matter of their identity.

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Mycologists have acquired the habit of calling cystidia "sterile cells" on the hymenium. This is thoughtless, and I can only assume that they do it because they read it in a thoughtlessly written book as an undergraduate and then never thought about it again. Presumably, these books call cystidia "sterile" because they don't produce spores (as opposed to the basidia). If so, then all the other types of cells on the hymenium also need to be called sterile, and so does the entire mycelium of the fungus. Come on, people: not bearing spores is the default condition for hyphae, not a special one; as such, it needs no special mention.

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