Ascocarp

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Diagram of an apothecium showing sterile tissues as well as developing and mature asci.

An ascocarp, or ascoma (plural: ascomata), is the fruiting body of an ascomycete fungus. It consists of very tightly interwoven hyphae and may contain millions of asci, each of which contains typically eight ascospores. Ascocarps are most commonly bowl-shaped, but may take on a number of other designs.

[edit] Classification of ascocarps

The ascocarp is classified according to its placement (in ways which are not fundamental to the basic taxonomy). It is termed epigeous if it grows above ground, as with the morels, whilst underground ascocarps, such as truffles are hypogeous.

The form of the hymenium is divided into the following types (which are important for classification). Apothecia can be relatively large and fleshy, whereas the others are microscopic — about the size of flecks of ground pepper.

Apothecium: here the ascocarp is open above like a cup. The fertile layer is free, so that many spores can be dispersed simultaneously. The morel, Morchella, an edible mushroom favored by gourmets, is a mass of apothecia fused together in a single large structure or cap. The genera Helvella and Gyromitra are similar.

The ascocarp of a morel contains numerous apothecia.

Perithecia of Nectria

Cleistothecium: in this case the ascocarp is round with the hymenium enclosed, so the spores do not automatically get released, and fungi with cleistothecia have had to develop new strategies to disseminate their spores. The truffles, for instance, have solved this problem by attracting animals such as wild boars which break open the tasty ascocarps and can spread the spores inside over a wide area. Cleistothecia are found mostly in fungi which have little room available for their ascocarps, for instance those which live under the bark of trees or under the ground like truffles. Also the dermatophyte Arthroderma forms cleistothecia.

Diagram of a perithecium. The ascospores (green) are in 8 pairs in each ascus.

Perithecium: this has the shape of a skittle or a ball. Its distinguishing feature is that on top it has a small pore, the ostiole, through which the spores are released one by one when ripe (in contrast to apothecia where they are released together). Perithecia are found for example on Xylaria (Dead Man’s Fingers, Candle Snuff) and Nectria.

Pseudothecium: this is similar to a perithecium, but the asci are not regularly organised into a hymenium and they are bitunicate, having a double wall which expands when it takes up water and shoots the enclosed spores out suddenly to disperse them. Example species are Apple scab (Venturia inaequalis) and the horse chestnut disease Guignardia aesculi.