Subdivision: Ascomycotina
line
Ascomycetes - (The Sac Fungi)
line
This is a large and diverse group, which is characterised by the formation of club-shaped cells or Asci, within which the ascospores are formed. Of the 2000 known genera only a small number produce visible fruiting bodies, and only some of these are covered in these web pages.
Cookeina colensoi
line
Reproduction
line
AscomycetesThe ascospores are a result of fusion between two nuclei either from the same individual or from two different but compatible mating strains. Meiosis follows fusion to produce four nuclei embedded in a common cytoplasm (the young ascus). In some species the cytoplasm becomes condensed around the nuclei to form four ascospores, but more commonly a mitotic division takes place to form eight nuclei resulting in the formation of eight ascospores. In some species a series of mitoses divisions follow one another resulting in the formation of twenty-four, thirty-two, sixty-four or more ascospores inside a much-inflated ascus.

As ascospores are usually forcibly shot some distance from the ascus, the hymenium therefore develops on top of the ascocarp facing upwards, and outwards or is spread over the surface of variously shaped structures. Ascomycetes are more numerous then Basidiomycetes, but few of them produce visible fruiting bodies.
Photos taken through
a microscope


Asci


Closer view of the Asci
line
Classification
line
Ascomycetes are divided into a number of classes. Those, which produce large fruiting bodies, are classified as Euascomycetes, which have unitunicate asci, each ascus with a single wall. Euascomycetes are then divided into 6 different orders based upon the shape of the ascocarp. Only two of which are covered here.

Discomycetes in which the asci are exposed on dish shaped ascocarps (apothecia).
Pyrenomycetes in which the asco-carps are bottle-shaped enclosing the asci.
 
line
Class: Euascomycetes (Unitunicate asci)
line
Ascomycetes of this class have the ascus wall composed of a single layer (unitunicate). Inside each ascus flask eight ascospores develop, bathed in a fluid, which is retained under pressure. When the spores are ripe, the neck of the ascus is designed to open with shock stimulus. This is achieved either by opening of a lid (operculum), or they may simply burst or break at maturity. A raindrop falling on the cup surface usually triggers this. The spores are then forcibly discharged out into the damp air currents. 
line
Subclass: Discomycetidae (Cup Fungi)
line
The asci are borne in a fertile layer or hymenium exposed in a cup or saucer-shaped fruit body known as an apothecium. Members of this group may have either operculate or inoperculate asc.
i.
 Order: Helotiales
  Family: Bulgariaceae
Family: Cyttariaceae
Family: Leotiaceae
Family: Geoglossaceae
Family: Helotiaceae
 Order: Pezizales
  Family: Discinaceae
Family: Pezizaceae
Family: Pyronemataceae
Family: Sarcoscyphaceae
Family: Sarcosomataceae


Paurocotylis pila


Leotia lubrica
line
Subclass: Pyrenomycetidae
line
Cylindrical asci are borne in a layer lining the inside of a flask-shaped structure opening by a pore or ostiole at the top, called the perithecium. In many types the perithecia themselves are embedded in sterile tissue known as a stroma, many of which make up one ascocarp.
 Order: Xylariales
  Family: Xylariaceae
 Order: Hypocreales
  Family: Hypocreaceae
Family: Clavicipitaceae
 Order: Sordariales
  Family: Lasiosphaeriaceae
 Order: Eurotiales
  Family: Trichocomaceae


Daldinia childiae


Xylaria hypoxylon
line
Related Links
line
AscomycotaOperculate Discomycetes - the Pezizales
 
line
 
line
The Hidden Forest | Forest Fungi | Site Map
Top