Structure of a Mushroom

An average mushroom is made up of about 90% water. It is for this reason that it has a short lifespan and soon decays. The flesh is made up of hyphae, similar to the mycelium. This apparently simple construction of hyphae can however produce a wide range of structure and size.

FACT: Africa has a mushroom species called Termitomyces titanicus which can grow more than 1 metre across, unlike thread fungi of some tropical rainforests which have caps less than 1mm across!

The Cap: protects the underlying spore producing gills, mainly from rain. Hyphae grow out at the top of the button and spread radially upward then downward. As the cap expands so the edge separates from the stem, causing the underlying gills to be exposed. The cap surface can then develop specialised structures and pigments.

The Stem: keeps the cap raised above the ground material so the spores can be dispersed by the wind. It is the first structure formed but does not lengthen until after the cap/gills are fully formed. The stem can be tall and cylindrical or short and squat, though is generally characteristic for each genus.

The Gills: are thin, vertical, radiating plates on the underside of the cap, (though Boletales, have pores rather than gills), originating as ridges from the stem apex. Sometimes lamellulae (secondary/tertiary smaller gills) are formed. The surface of the gills are covered with a spore producing layer known as the hymenium. While the young gills are formed, the region is protected by one or more veil layers. At maturity, gills may be widely spaced to densely crowded. Mushrooms can be identified better by looking at there mode of gill attachment to the stem apex. (see diagram on left)

Veil Layers: are present in some mushrooms when one or two protective mushrooms may cover the immature fruitbody. On the stem of a mature mushroom, these are reduced to a ring (annulus), or loose scales on the cap surface. The full compliment can be found on some species of Amanita. The universal veil (Velum universale) envelops the immature fruitbody but on expansion it breaks down, forming the cap scales and a cup like volva at the stem base. The partial veil (Velum partiale) links the cap margin to the stem apex, covering the immature gills, breaking down to form the stem ring. Fruitbody development types are based on the layers shown on the right.