Ascocarp

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An ascocarp, or ascoma (PL: ascomata), is the fruiting body (sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are most commonly bowl-shaped (apothecia) but may take on a spherical or flask-like form that has a pore opening to release spores (perithecia) or no opening (cleistothecia). [1] [2] [ better source needed ]

Contents

Classification

Ascomata.svg
Tissue arrangement. The peridium is indicated in pink. Note the cylindrical asci in the two left types (apothecium, peri-/pseudothecium), and the globose asci in the two right types (cleistothecium, gymnothecium).
Ascomata relative.svg
Relative sizes of apothecium, peri-/pseudothecium and cleisto-/gymnothecium (from left to right).

The ascocarp is classified according to its placement (in ways not fundamental to the basic taxonomy). It is called epigeous if it grows above ground, as with the morels, while underground ascocarps, such as truffles, are termed hypogeous. The structure enclosing the hymenium is divided into the types described below (apothecium, cleistothecium, etc.) and this character is important for the taxonomic classification of the fungus. Apothecia can be relatively large and fleshy, whereas the others are microscopicabout the size of flecks of ground pepper.

Apothecium

Diagram of an apothecium showing sterile tissues as well as developing and mature asci Ascocarp2.png
Diagram of an apothecium showing sterile tissues as well as developing and mature asci

An apothecium (plural: apothecia) is a wide, open, saucer-shaped or cup-shaped fruit body. It is sessile and fleshy. The structure of the apothecium chiefly consists of three parts: hymenium (upper concave surface), hypothecium, and excipulum (the "foot"). The asci are present in the hymenium layer. The asci are freely exposed at maturity. An example are the members of Dictyomycetes. Here the fertile layer is free, so that many spores can be dispersed simultaneously. The morel, Morchella, an edible ascocarp, not a 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. Smardz-Morchella-Ejdzej-2006.jpg
The ascocarp of a morel contains numerous apothecia.

Cleistothecium

A cleistothecium (plural: cleistothecia) is a globose, completely closed fruit body with no special opening to the outside. The ascomatal wall is called peridium and typically consists of densely interwoven hyphae or pseudoparenchyma cells. It may be covered with hyphal outgrowth called appendages. The asci are globose, deliquescent, and scattered throughout the interior cavity i.e. as in Eurotium or arising in tufts from the basal region of ascocarps as in Erysiphe. 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 spread the spores over a wide area. Cleistothecia are found mostly in fungi that have little room available for their ascocarps, for instance those that live under tree bark, or underground like truffles.

Gymnothecium

Similar to a cleistothecium, a gymnothecium is a completely enclosed structure containing globose or pear-shaped, deliquescent asci. However, unlike the cleistothecium, the peridial wall of a gymnothecium consists of a loosely woven "tuft" of hyphae, often ornamented with elaborate coils or spines. Examples are the Gymnoascus , Talaromyces and the dermatophyte Arthroderma .

Perithecium

Perithecia of Nectria Nectria.jpg
Perithecia of Nectria

Perithecia are flask shaped structures opening by a pore or ostiole (short papilla opening by a circular pore) through which the ascospores escape. The ostiolar canal may be lined by hair-like structures called periphyses. The unitunicate asci are usually cylindrical in shape, borne on a stipe (stalk), released from a pore, developed from the inner wall of the perithecium and arise from a basal plectenchyma-centrum. Examples are members of Sphaeriales and Hypocreales. Perithecia are also found in Xylaria (Dead Man's Fingers, Candle Snuff), Nectria , Claviceps and Neurospora .

Sometimes the perithecia are "free" (individually visible from the outside), but in many species they are embedded in a dense sterile tissue of haploid cells called a stroma (plural: stromata). [3]

Pseudothecium

Perithecium no text.PNG
Diagram of a pseudothecium. Eight ascospores (green) are typically present in each ascus.
Leptosphaerulina sp.jpg
Bitunicate asci in the pseudothecium of Leptosphaerulina sp.

This is similar to a perithecium, but the asci are not regularly organised into a hymenium and they are bitunicate, having a double wall that 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.

See also

Related Research Articles

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On upper and under surfaces of leaves, leaf-stalks and branches; forming densely crowded, minute, black, generally orbicular, often confluent, easily detachable, brittle crusts, with surface of leaf beneath of a pale brown or pale reddish colour. Mycelium composed of an interosculating network of delicate, colourless, septate, luxuriantly branched hyphae, about 3 μ broad, and attached to matrix, gradually passing into the stouter coloured hyphae above it. Coloured hyphae dark brown, rigid, thick-walled, closely interwoven, septate, branched, 8-9½ μ broad, ultimate branchlets generally 1-septate, knobbed and paler in colour. Perithecia seated on crust in clusters, depressedly globose, black, rough with warty spines, 130-330 μ, the latter being the average full-grown size. Asci oblong to cylindrical, 4-spored usually, 38-64 X 13-26 μ (immature). Sporidia brown, oblong, 4-septate, slightly constricted at septa, rounded at both ends, 36-44 x 14-15 μ. Pycnidia globose, golden-brown, opening by circular mouth and wall composed of small polygonal cells 100-140 μ, along with perithecia. Sporules minute, subglobose or oval, hyaline or rarely brownish, 5½ x 3 μ or 4 μ diameter borne, on delicate hyaline, septate, branched hyphae.

On Solanum viride, R.Br.; Tintenbar, N.S.W. (Maiden).
The crusted mycelium is readily removed, and is steel-grey on the attached surface.

The asci when ripe seem to burst within the perithecium, hence the difficulty of getting a mature ascus. The sporidia, which are at first colourless, then greenish and finally brown, often germinate even within the perithecium either from one or more segments. They are stained greenish-yellow by potassium-iodide-iodine, and the other contents of the perithecia are similarly stained.

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References

  1. "ascocarp (fruiting structure of fungi)". Encyclopædia Britannica . Retrieved 23 November 2020.
  2. "Atlas of Clinical Fungi (glossary)". Westerdijk Fungal Biodiversity Institute. Archived from the original on 28 October 2019. Retrieved 11 September 2019.
  3. See page 30 and glossary of Læssøe, H.; Petersen, Jens (2019). Fungi of Temperate Europe. Princeton University Press. p. 30. ISBN   9780691180373.