II. Class Homobasidiomycetes

Produce the familiar mushrooms, conks, puffballs, and stinkhorns. In the Homobasidiomycetes, the basidia are uniformly single clavate cells. Usually four basidiospores are formed in each basidium which are forcibly discharged. The basidiospores germinate and give rise to hyphae only. The vegetative mycelium has dolipore septa and bears clamp connections in many species. A definite fruitng body is formed in all of the orders. Many of these fungi are found on soil, dung, and decaying wood.

We will consider the two informal 'classes' - Hymenomycetes and Gasteromycetes in our study of the Homobasidiomycetes (remember the Hymenomycetes includes members of both the Homobasidiomycetes and Heterobasidiomycetes). Note that the orders in this class are not monophyletic. There are several members of the order Agaricales that are more closely related to some members of the order Aphyllophorales than to other agarics.

A. ORDER AGARICALES

The Agaricales have the basidia borne on basidiocarps that are fleshy and decay away after maturity. The basidiocarp is usually capitate, with a stipe, and the basidia are borne on gills, in pores, or in rare cases, on a smooth surface. The basidia are two- to eight-spored, and the basidiospores are forcibly discharged at maturity. The basidiospores are one-celled. The boletes are often recognized to belong to a distinct order because they have tubes rather than gills, although they are fleshy and otherwise like the Agaricales. Many agarics form mycorrhizal associations with forest trees and shrubs while a great number are saprophytes. They are important food for animals and humans and have played interesting roles in the history of some cultures. This is a big order and we will only consider a few families and species.

1. FAMILY BOLETACEAE

The hymenium of members of this family line pores on the underside of a fleshy pileus.

Boletus-the hymenium is distinctly poroid and the stipe is not hollow, and the pileus is not viscid (sticky or gelatinous due to the hyphal absorption of water). Examine available specimens of Boletus spp. and note the characteristic features.

2. FAMILY RUSSULACEAE

This family is characterized by rounded to depressed caps and gills composed of large round cells intermixed with regular cellular hyphae. The pileus also contains sphaerocysts and the flesh is usually brittle and dry.

Lactarius - In this genus latex is present in the basidiocarp. Examine preserved specimens of different species.

Russula - Latex is absent in the basidiocarp of this genus. Examine available specimens.

3. FAMILY AGARICACEAE

Mushrooms in this family are usually fleshy with rounded or flattened caps, which range in color from white to brown or gray-brown. The gills are free, white to gray or pink to dull chocolate brown to purple brown. The stalks are relatively thick with an annulus typically present. Spores are purplish brown to dark brown. Members of this family occur in a number of habitats including lawns and pastures, humus and litter in hardwood and conifer forests, and manured areas. They often resemble the white Amanitas in early development, thus it is important to examine the entire mushroom.

Agaricus brunnescens - This is also called A. bisporus and A. campestris var. bisporus. This is the mushroom grown for commercial use and what you usually buy from grocery stores. It is characterized by having two spored basidia. Examine specimens of various ages. Mount a small portion of a gill in water and look for basidia under the microscope.

4. FAMILY AMANITACEAE

All mushrooms in this group develop from an oval to round structure (button) covered by a universal veil, which breaks when the the mushroom stalk elongates. This is illustrated in the attached figure. Spores are oval to round, smooth and thin-walled and the spore prints are white to cream colored. An inner veil is also typically present. This family also includes the most poisonous mushrooms and accounts for most deaths due to mushroom poisonings in the United States.

Amanita - In this genus a volva is typically present. Examine available specimens. A. verna, A. virosa - These species are pure white and have a sac-like volva, white annulus and smooth cap. Both are very poisonous, usually deadly. These are also known as the destroying angel. A. muscaria (the fly agaric) - This species has yellow to reddish caps with veil patches. The volva consists of several concentric rings above the bulb. This is also a poisonous species.

5. FAMILY COPRINACEAE

This family is characterized by thin, typically conical caps with nearly free to attached to notched gills and brown to black spore prints. They are saprobes on dung, wood debris, or humus in lawns. Some species are edible but some have been linked to gastrointestinal upsets.

Coprinus - In this genus, the gills and cap are converted into an inky mass by autodigestion, hence the name, 'inky caps' for many species. Examine preserved specimens of common species, then examine prepared slides showing sections of gills; look for basidia.

6. FAMILY TRICHOLOMATACEAE

This is a large and diverse mushroom family, all genera of which have white to lilac or yellowish spore prints and attached gills. There are edible and poisonous members of this family.

Armillaria- The pileus are fleshy and easily broken and they occur in clusters on wood, in which black rhizomorphs are often found.

Armillaria mellea -This is the honey mushroom characterized by the presence of an annulus. This is a parasite of trees. Examine preserved fruiting bodies, mycelial fans and rhizomorphs of available specimens.

Pleurotus - This genus occurs on wood and the stipe is eccentric or lacking. The cap is smooth, as are the gill edges. The pileus is shell-shaped to fan-shaped and are broad, hence the name 'oyster mushroom'. This is a delicious edible mushroom that is easily recognized by beginning collectors. Examine photographs of P. ostreatus. We hope to see this mushroom from our bag cultivation.

B. ORDER APHYLLOPHORALES

This order includes those Hymenomycetes which do not have gills on the fruiting body. The basidiocarp varies in form from appressed, to resupinate, pileate, clavate, or collarioid. The hymenial surface may be smooth, may form teeth or pores. In many species the fruiting body is persistent and tough or woody. The basidia are arranged in a hymenium and the basidiospores are forcibly discharged. The Aphyllophorales are mostly saprobic on soil, wood, or litter, but some are parasites on trees, on which they form an external basidiocarp.

1. FAMILY POLYPORACEAE

The basidiocarp of members of this family is resupinate to pileate, sessile to stipitate, annual or perennial. The hymenium is poroid from the first and the spores are usually smooth.

A. Ganoderma - This genus has usually stipitate basidiocarps, with a tubular hymenium. The spores are bworn, ellipsoid, echinulate, and truncate at one end at maturity. The surface of the sporophore often has a varnished appearance. Examine specimens of common species.

B. PolyporusPolyporus are annual and vary from resupinate to stipitate. The hymenophore is poroid. Examine the prepared slides showing sections through pores of Polyporus sp. Look at the sporophores of available species.

C. ORDER LYCOPERDALES

Members of this order include the typical puffballs, the chief representative of a group of orders informally known as the 'gasteromycetes'. The basidia are enclosed within a central mass called a gleba and the basidiospores are not forcibly discharged. The gleba is usually enclosed within a peridium and powdery. The hyphae are dolipore septate with or without clamp conncetions. The fruiting bodies range in size from barely visible with the naked eye to the largest of all fungi. They are usually saprobic on soil or wood.

1. FAMILY LYCOPERDACEAE

The peridium of this family may consist of several layers with the outermost one being persistent.

Lycoperdon - The fruit bodies of Lycoperdon are medium size and grow on the ground or sometimes on wood. The exoperidium is roughened and the endoperidium has an apical pore through which the spores escape. Examine the prepared slides showing a section through a sporophore of Lycoperdon sp.

Calvatia - the fruiting bodies are often large and occur on the ground. The spores are released by falling away of the upper part of the peridium. Examine specimens of available species.

2. FAMILY GASTRACEAE

The exoperidium of this family consists of three layers which open by stellate dehiscence.

Geastrum - This genus contains the earth stars species. The endoperidium is paper-like and persistent with an apical ostiole. The gleba has a prominent pseudocolumella of highly compacted capillitium. Examine specimens of Geastrum and note how the exoperidium separates into stellate sections.

D. ORDER NIDULARIALES

In the Nidulariales the fruiting body grows on the ground or on organic debris. The peridium consisting of one to many layers is firm and cup-shaped. The gleba consists of one to many hard egg-shaped peridioles, and the spores are smooth, hyaline, thick-walled, and often large.

1. FAMILY NIDULARIACEAE

Cyathus - This is also known as the bird's-nest fungus. Examine dried specimens of Cyathus and see for yourself why it is called the bird's nest fungus. Examine the prepared slide showing sections through a sporophore of Cyathus sp.

NOTE: There will be several books with good pictures to help you become familiar with the different species in this class of Basidiomycota. You are encouraged to flip through them. There are several species which we cannot cover in class and obviously, fresh specimens will be hard to collect at this time of the year. Most of you have been introduced to these fungi in our Mt. Lemmon field trip and through some specimens we brought in class early in the semester.

TERMS TO KNOW

clavate - club-shaped

capitate - having a cap or pileus (syn. pileate)

poroid - having pores (as opposed to having gills)

viscid - sticky or gelatinous, usually for mushrooms with hyphae that absorb water

sphaerocysts - spherical cells present in the cap of the Russulaceae

resupinate - lying flat on the substratum with the hymenium on the free surface

collarioid - coral-shaped or sometimes clustered finger-like or lace-like branches

stipitate - having stalks or stipes

reticulate - having the form of a net; covered with net-like ridges

truncate - with ends appearing cut-off thus horter than normal size