Basidiomycetes
The class Basidiomycetes includes those members that produce their basidia and basidiospores on or in a basidiocarp. The morphology of the basidium is variable. Until recently the morphology of the basidium was believed to be a key to determining relationship in the Basidiomycota. Basidial morphology was once the basis for classifying the fungi to class or subclass. However, rDNA sequencing analyst (Swann and Taylor, 1993), septal pore morphology and cell wall biochemistry (McLaughlin et al, 1995) have determined that far too much emphasis was placed on this characteristic and all members of the Basidiomycota that produce basidiocarps are now included in a single class, the Basidiomycetes, and the morphology of the basidiocarp and basidium are characteristics that are now used to classifying fungi into the various orders of this class.
Order: Agaricales
This is the order of Basidiomycetes with which
most of us are familiar. This is the order that is commonly referred to as mushrooms.
Basidiocarps of this order typically are "fleshy" and have a stipe
(=stalk), pileus (=cap), and lamellae (=gills) where the basidia and
basidiospores are borne (Fig. 1-4). The Basidiospores in this order of fungi are forcibly
ejected from the basidium, into the area between the lamellar edges, which then allows the
spores to fall free from the mushroom and be dispersed by wind. A demonstration of this
mechanism can be observed here. See also: Spore Dispersal.
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Figure 1: Typical mushroom of Agaricales: Stipe, annulus, lamella and pileus. Basidia and basidiospores are produced in an hymenium on the lamella surface. |
The mushroom life cycle will be used as representative of the basidiomycete life cycle. Although clamp connections are present in the dikaryon of some species of, they are also absent in many. Clamp connections are believed to function in ensuring that each cell has a compatible pair of nuclei. The formation of a clamp connection is described here.
Some examples of of Agaricales that occur in
Hawaii (Fig 5-9):
Order: Aphyllophorales
Species in this order are often coriaceous,
leathery to woody, but may also be fleshy. The basidiocarps and hymenia are more variable
than in the Agaricales. Examples of members of this order can be observed below (Figs.
10-14). As in the case of the Agaricales, the basidiospores are forcibly ejected from the
basidium and are then dispersed by wind.
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