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16.3: Macrofungi

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  • Ascomycota -- The Sac Fungi

    This group of fungi is when the life cycle starts to get particularly strange and the fungus forms something called a dikaryon (di- meaning two, karyo- meaning nucleus). When two different hyphal bodies fuse, they do not fuse their nuclei, only the cytoplasm. The result is a single fungal body with two separate types of nuclei floating around inside it. Because it is neither haploid (n), nor truly diploid (2n), this condition is called being dikaryotic (n+n).

    Ascomycota are distinguished from other groups of fungi by the following characteristics:

    • Production of ascospores (usually 8) within an ascus, a normally elongate, sac-like structure
    • Hyphae with simple septations
    • The mycelium is primarily haploid. When two haploid (n) mycelia of the correct mating types meet, they can form a dikaryotic (n+n) fruiting body called an ascocarp.

    There are three different types of ascocarps:

    1. Apothecium - a (usually) cup-shaped fruiting body with asci lining the interior of the cup. Two exceptions are Helvella and Morchella (morels), where the cup has been inverted, no longer looking like a cup, and the asci cover the now-exterior surface.
    2. Perithecium - a round fruiting body with a long neck, much like a bottle, with the asci inside the bottom of the bottle. Microscopic and quite similar to a Fucus conceptacle.
    3. Cleistothecium - a spherical, enclosed fruiting body packed with rounded asci. These are also microscopic and can be beautifully ornamented.
    Figure \(\PageIndex{1}\): Peziza Asci

    Above is the spore producing surface of an apothecium. The long asci each contain 8 ascospores.

    Observe the ascomycetes on display. What type of ascocarps do you see? Draw and label them below, indicating where the asci would be found.

    Make a thin section slide of Xylaria using KOH for the wet mount. Draw a perithecium below. Label an ascus and ascospores.

    Make a thin section slide of an apothecium. Draw it below, labelling an ascus and ascospores. Can you find septations in the hyphae?

    If available, view a cleistothecium from the Erysiphales (powdery mildews) under both the dissecting and compound microscope. Draw it below, labelling an ascus and ascospores.

    Basidiomycota -- The Club Fungi

    Basidiomycota are the other group of dikaryotic fungi. This group includes the mushroom-forming species of fungi, as well as two groups of (mostly) plant parasites, delightfully referred to as the rusts and the smuts.

    Basidiomycota are distinguished from other groups of fungi by the following characteristics:

    • Basidiospores (usually 4) produced from a basidium--a normally squat, roundish structure with prongs called sterigmata that spores are produced on.
    • Hyphae with complex septations. These specialized septations look like they are surrounded by parentheses and help the mycelium maintain its dikaryotic state.
    • Clamp connections can sometimes be seen, though are only obvious in certain genera.
    • The mycelium is primarily dikaryotic. The haploid spores germinate and must find another germinating spore of the correct mating type to form a dikaryotic mycelium. This can then produce fruiting bodies called basidiocarps, or as we commonly call them, mushrooms.
    Figure \(\PageIndex{2}\): Coprinus Basidia

    The image above shows the spore producing surface of a basidiomycete, Coprinus. The dark football-shaped structures are the haploid basidiospores. They sit atop small projections called sterigmata (sterigma, singular) that emerge from the top of the basidium. In most mushrooms, each basidium produces four basidiospores.

    Based on the presence of four haploid spores, which type of cell division do you think formed these spores and why?

    How could you explain the presence of 8 spores in ascomycetes?

    Label the anatomy of an Amanita muscaria basidiocarp below, including the cap (pileus), universal veil scales, gills (lamellae), annulus, stipe, volva, and mycelium.

    Figure \(\PageIndex{3}\): Amanita muscaria mushroom

    Not all basidiocarps look like Amanita muscaria. Observe the diversity of basidiomycetes on display. In the space below, draw and label a jelly mushroom, a coral mushroom, a bracket, and a puffball.

    Make a thin section of a gilled mushroom, using 5% KOH for the wet mount. Try to find basidia and basidiospores. Can you see clamp connections? It may help to stain with Phloxine B. Draw and label what you see below.

    The phylum Basidiomycota is composed of three major groups. All of the fungi above are from the subphylum Agaricomycotina. The two other groups are composed of primarily parasitic fungi, rusts (Pucciniomycotina) and smuts (Ustilaginomycotina). View the available prepared slides of these fungi and draw what you see below. Can you find basidia and basidiospores? Compare and contrast what you see with the Agaricomycetes.

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