Fungal Morphology: The Parts of a Mushroom

Fungi differ significantly in their size and shape, from tiny single-celled yeasts to the largest living organism on Earth, the honey mushroom. And within this kingdom, the most familiar organisms are certainly the wide variety of mushrooms that exist. Given the incredible diversity of mushroom species, it is crucial to know the general structure of a mushroom in order to accurately identify a species when encountered. For this reason, the best way to begin our study will be to discuss the morphology, or structure, of a mushroom. Here is a beautiful bright orange and red mushroom species, Amanita jacksonii.

The European variety is commonly known as Caesar’s mushroom because it was enjoyed by Roman Emperors. However, it can be confused with many poisonous fungi. We are currently looking at the fruiting body, or the sporocarp, of this mushroom. The fruiting body accounts for the reproductive function of a fungus and can vary significantly between fungal species. When you see a mushroom in the wild, or even in a market, you are looking at the fruiting body, while you only see a small portion of the actual fungus. Underneath the soil, there is a filamentous network that supports the fungus. These filaments consist of thin fibers called hyphae, and the collective network of hyphae is known as the mycelium.

The mycelium allows for nutrient acquisition, growth of the fungus, and production of the fruiting body. Many mushrooms form a symbiotic relationship between the mycelium and plant roots called mycorrhizae, as we touched upon in the botany series, with myco meaning mushroom and rhiza or rhizo meaning root. Mycorrhizae represent an amazing interaction that allows for the growth and life of many plants and mushrooms. Now, although some fungi can be beneficial for the organisms they interact with, some mushrooms retrieve nutrients through the breakdown of other living organisms. This is known as a parasitic relationship. For example, these are cordyceps fungi that have infected and killed these insects.

However, not all fungi have their mycelia networked with living organisms. Fungi that decay dead organic matter such as leaf litter or rotting wood are known as saprobic fungi. Let’s return to Amanita jacksonii. Any fruiting body of a mushroom is formed from dense bunches of hyphae. When a mycologist looks at a mushroom fruiting body, they look at the presence of or lack of different characteristics of the structure in hopes of identifying the species. The top portion of the mushroom is called the pileus or the cap. On the underside of the pileus, there are thin ribbon-like projections called lamellae or gills. The lamellae are the site of spore production for this specific fungus. However, many other mushroom varieties have different structures that act as the site of spore production. We call the tissue layer of spore production in a fungus, the hymenium.

The spores in a fruiting body allow for sexual reproduction of the fungus. This part holding the pileus or cap is called the stipe or the stalk. At the base of the mushroom, there is a white cup encasing the stipe. This is called the volva or universal veil. The universal veil houses the immature fruiting bodies of mushrooms. As you can see here, the maturing mushroom sprouts from the universal veil. The ring of tissue below the cap and gills is called the annulus or partial veil. It covers the hymenium throughout development and then detaches from the hymenium once the fruiting body matures. When identifying mushrooms, many of these traits can be of assistance in identifying species. Let us use our new knowledge of these structural components to identify another mushroom. This mushroom’s cap is white and smooth. It has white gills on the cap’s underside.

The stipe is white, and a partial veil is present. At the base of the stalk, a white universal veil is present. A mushroom with these characteristics can only be one thing, the death angel, Amanita bisporigera. The death angel is an extremely deadly mushroom that produces a poison called amatoxin that causes liver failure if ingested. Many mushrooms within the Genus Amanita produce amatoxin. In general, if the mushroom has gills, a partial veil, and a universal veil, it is likely a species from the Amanita genus. When trying to identify any mushroom, we look at structural traits such as the cap, stipe, and gills. There are variations to each of these structures, and many of these variations have descriptions that are outlined in any mushroom identification resource. But these macroscopic features of a mushroom can only get you so far in mushroom identification.

Many mushrooms require the observation of microscopic features to be accurately described. Mycologists will look at the gills or other spore producing structures to see the hyphal tissue called the trama, the spore-producing cells, and the spore shape and size in order to accurately identify a species. Naturally, this process requires a microscope. However, an easy method to assist in the identification of mushrooms is to create a spore print. By placing a mushroom with the gills faced down on a piece of printer paper, aluminum foil, or wax paper, the spores will be released from the mushroom cap and fall onto the surface of the paper. This produces the spore print which shows the color of the spores. The spore color can be a key identifying trait that is especially useful when searching for edible or medicinal mushrooms. Not all fruiting bodies of fungi have a spore-producing structure that forms gills. We call any spore-bearing structure, or hymenium bearing structure, the hymenophore.

So, Amanita jacksonii, being a gilled mushroom, would have a lamellate hymenophore. Boletus edulis, or the porcini mushroom, forms spongy pores on the cap’s underside instead of gills, so mycologists describe its hymephore as tubular. Many shelf fungi or polypores have a hymenophore that forms into pores on the underside of the cap. This is the reishi mushroom from the genus Ganoderma. It is considered a polypore mushroom and is also considered a medicinal fungus.

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