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spore

(pl. spores)

Terms discussed: ascospore (pl. ascospores), basidiospore (pl. basidiospores), chlamydospore (pl. chlamydospores), endosporium, episporium, exosporium, mesosporium, peripheral envelope, perisporium, zygospore (pl. zygospores)




Image of Cantharellus from Joseph Henri Léveillé (1837) Sur le hymenium des champignons in Annales des Sciences Naturelles. Botanique
Cantharellus
The spore is the basic reproductive unit of a fungus. It serves the same role in the fungal life-cycle that seeds do in the life-cycle of a plant. The difference between a spore and a seed is that a seed contains an embryo, a tiny miniature plant. A spore, on the other hand, contains only genetic material, completely undifferentiated. Spores have proven to be a popular reproductive strategy, used by mosses, oomycetes, slime molds, and other more exotic creatures - - all the kingdoms, in fact, except for animals.

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Septate Antennaria spores
Antennaria
Most spores are only a single cell, but some fungi have spores that are divided into more than one cell. The spores of this Antennaria are also considered ascospores, since they are grown in asci. Spores grown on basidia are known as basidiospores. The other most common or standard type of spore, the conidium, is discussed separately.

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Image of Asterophora parasitica from Christian Gottfried Daniel Nees von Esenbeck & A. C. F. Henry (1837) Das System der Pilze: part one
Asterophora parasitica
Chlamydospores are a specialized type of spore: they are larger than the standard spores produced by that fungus, and have a very thick wall. Chlamydospores are usually darkly pigmented; here the caps of the smaller mushrooms are breaking up into a brownish powder composed of chlamydospores. Chlamydospores can be asexual (and technically, thus, a kind of conidium), or sexual.

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Image of Zygomycetes from Christian Gottfried Daniel Nees von Esenbeck & A. C. F. Henry (1837) Das System der Pilze: part one
Zygomycetes
A zygospore is a special type of chlamydospore arising from sexual conjugation between two fungi. In addition to being thick-walled and darkly colored, a zygospore is usually heavily ornamented as well, with many spines or ridges. It is formed between two specialized organs called suspensors, which are themselves usually heavily ornamented, one from each mating partner. The zygospore forms between them and then breaks away, a process which is illustrated in #3-5 of the picture. Zygospores give their name to an entire phylum of the kingdom of fungi, the Zygomycota. Zygospore formation was the first activity to be used as evidence for sexuality in fungi.

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"Normal", sexual spores are haploid, or, more accurately monokaryons. I assume that conidia, chlamydospores, and zygospores are also monokaryons, but there's no logical reason they couldn't be dikaryons. I don't know of any place where this question is addressed.

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Image of Tulostoma from Jean Louis Émile Boudier (1904 - 1909) Icones mycologicae ou iconographie des champignons de France, principalement Discomycètes
Tulostoma
Sometimes the spore wall has several layers. Of these the endosporium is the innermost, and is usually quite thin. Sometimes the developing spore is enveloped by a membrane called a perisporium, which usually sloughs off as the spore matures; R. Heim, in his R. Heim (1931) Le genre Inocybe that this should be called the peripheral envelope instead, at when talking about Inocybes. The episporium is considered the fundamental layer of the spore wall; it is the thickest, gives rise to whatever ornamentation there is, and is also responsible for the spore's color. The mesosporium sometimes occurs, in between the episporium and the endosporium; and the exosporium sometimes covers the episporium (and is pierced by its ornamentation) but is in turn covered by the perisporium.

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