Ascomycota, Ascomycetes & Sac Fungi

The order Sphaeriales has a true peridium and perithecial wall that is either brown or black in color. The texture is carbonaceous or brittle. The ascus has rather thin lateral walls and relatively a thick apical wall. Several members have perithecia scattered over a mycelial mat. The grouping into families has varied, but the present discussion includes eight: Chaetomiaceae, Fimetariaceae, Ophiostomataceae, Gnomoniaceae, Diaporthaceae, Allantosphaeriaceae, Xylariaceae and Phyllachoraceae. The order might appropriately be considered the "core group" of the Pyrenomycetes. Most of the Ascomycota that produce true perithecia are included and eventually all such fungi might be incorporated into the order. However, some of the genera are being transferred to the order Pseudosphaeriales. The forms that will most likely retain an enduring place in the Sphaeriales have typical flask-shaped perithecia. With slender asci and paraphyses lining the lower portion of the fruiting body cavity. The ascocarp wall is usually, but not always, dark, and most often brittle or leathery in texture. The perithecia may be borne separately and scattered on the mycelium, but they are sometimes produced in connection with a stroma in which case they are usually closely clustered. In many genera the perithecia grow completely imbedded in stromatic tissue, with only the ostioles protruding. Such perithecium-bearing stromata are typically dark brown or black and sometimes carbonaceous in texture at maturity. Many forms possess a conidial stage like in the Hypocreales.

The Family Chaetomiaceae is represented by the Genus Chaetomium. The ability to digest cellulose caused much difficulty with clothing during World War II. The perithecium is flask-shaped and sterile spine-like hairs project from the flask. Coiled appendages arise from the flask's neck. The asci are round and the ascospores are citriform (lemon-shaped) and they ooze out from slime at the neck.

The Family Fimetariaceae includes the orange-colored bread molds. The Genus Neurospora is a common laboratory contaminant and it has a history of being a serious pest in bakeries. The mycelium grows very rapidly. The cells are multinucleate and 1-4 days are required to complete the imperfect stage. The Monilia Imperfect Stage has branching conidiophores and a multicellular, multinucleate mycelium. There are branching chains of orange-colored conidia, which are often called macroconidia. These are easily dislodged by air currents.

The Perfect Stage is heterothallic where one mating type (A or B) produces both sex organs, but neither will mate with the same type. Spermatiophores are produced on all mycelia. These are flask-shaped structures, which form small, uninucleate cells at the base (= spermatia or microconidia). Neurospora is exceptional in that some of its spermatia may germinate directly. Protoperithecia are produced and contain a slightly coiled ascogonium that is multicellular and surrounded by a weft of hyphae. From the apex of the ascogonium there extends a relatively long tricoygyne, which may be branched and extended out some distance. The tricogyne is narrower than a hyphal cell, but has crosswalls and is multicellular.

The tricogyne grows toward the spermatium if it is of the opposite mating type. Presumably the nucleus of the tricogyne after fusion with a spermatium migrates down the tricogyne and joins with the ascogonium. Protoperithecia grow in size four hours after mating, and perithecia are found with asci after crozier formation.

Additional mating forms exist. Mating with a macroconidium may also be possible although the time for a reaction to the stimulus to show is extended here. Mating between hyphal cells is also possible. Ascospores are forcibly discharged from elongated asci and only one ascus at a time matures.

Additional characteristics of Neurospora are that the ascospores are small and the asexual cycle is completed in 1-2 days. The sexual cycle is completed in 1-10 days. The mycelium is haploid and all genetic markers appear and there is no masking by dominant genes. This is a phototrophic genus where all spores are thrown with equal force.

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Genetics in Neurospora

Neurospora sitophila and N. crassa have their asci formed in a single row; the assumed position corresponds to the order in which division took place (mitotic products). Thus, it is possible to isolate single ascospores to determine where meiotic processes occurred.

Neurospora tetrasperma was once thought to be homothallic but it is actually facultatively homothallic. Two nuclei are enclosed in a common cytoplasm. Then, usually four ascospores are formed. Each ascus contains both mating factors. Large ascospores are able to give rise to functioning perithecia (homothallic), while small ascospores are unable to do this and have only one nucleus each and are heterothallic.

In most cases crossing-over does take place.

When the nuclei do not lie close enough together separate haploid ascospores are cut out.

In the Family Xylariaceae the Genus Xylaria is sometimes referred to as "Dead Man's Fingers." There is an u0right branched or simple stroma. Perithecia line the outside of the stroma.

The Genus Hypoxylon has a flat cushion-shaped stroma and the Genus Daldinia has a round stroma with our without a stalk. Characteristic concentric rings occur in the stroma, which are not growth rings.

The Family Diaporthaceae is represented here by Endothia parasitica. These species wiped-out native American chestnuts, a far superior species than those occurring in Europe. Invading from the Orient it was first observed in America in 1910 in New York state. The mycelium of this fungus kills the chestnut cambium. The mycelium forms a stroma just under the surface of the bark. Perithecia are embedded, necks only, at the base of the stroma. These necks are very long and extend up through the stroma.

The Family Allantosphaeriaceae differs from the Diaporthaceae by having asci with a long, tapering, persistent stalk and they form a definite hymenial layer in the perithecium. Paraphyses are formed but they gelatinize by the time the perithecium is mature. The family gets its name from the ascospores that are usually sausage-shaped (allantoid). They are one to many-celled and they are brown in color when occurring in a mass. Most species are saprobic, inhabiting dead bark or wood, with a few species being also parasitic on some plant species.

In the Family Phyllachoraceae the Genus Phyllachora causes "Tar Spot" of grasses. In some species the perithecium practically fills the space between the cuticle and the epidermis. Stromatic layers are formed between the necks and bases of the perithecia.

The Family Ophiostomataceae includes some severe plant pathogens. The Genus Ceratocystis causes "Blue Stain" of wood. One notorious species, Ceratocystis ulmi, causes "Dutch Elm Disease" of American elm. It was first detected in North America in 1931. By the year 2000 over 98 percent of American elms were destroyed. The fungus is heterothallic and the scattered perithecia have extremely long necks. Ascospores are slightly curved and pushed outside in a gelatinous mass. The asci disintegrate early so that spores lie free in the perithecial wall.

In another Genus Ustulina a layer of perithecia occurs on a convoluted stroma.

The Family Gnomoniaceae have their perithecia buried in the substratum and each of them is provided with a prominent beak that protrudes from the surface and serves as an exit for the ascospores. The ascal walls of some species are much thickened at the apex of the ascus to form a narrow canal in the center through which the ascospores pass while being discharged. There are no paraphyses in the mature perithecia. Gnomonia leptostyle causes anthracnose of walnut and related plants. Gnomonia veneta causes sycamore anthracnose and G. ulmea causes leaf spot of elm. Gnomonia erythrostoma is the cause of cherry leaf scorch. The conidia of most species are produced in acervuli. However, G. fragariae on strawberry bears conidia in pycnidia.

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Please refer to the following plates for characteristic structures and Life Cycles in the Sphaeriales:

Ascomycota: Euascomycetes: Sphaeriales

Plate 128 = Sphaeriales: Ascocarp diagram.

Plate 129 = Chaetomium sp.: Ascospore maturation.

Plate 130 = Life Cycle -- Neurospora sitophila.

Plate 131 = Structures of Ophiostoma fimbriatum.

Plate 132 = Structures of Gnomonia ulmea: Perithecium & Ascus.

Plate 133 = Structures of Gnomonia fragariae.

Plate 134 = Structures of Phyllachora graminis: Stroma & perithecia.

Plate 205 = Life Cycle -- Pyrenomycetes: Sphaeriales: Neurospora sitophila

Plate 206 = Diagnostic Characters: Pyrenomycetes: Sphaeriales: Ceratocystis, Chaetomium, Daldinia, Neurospora,

Phyllachora, Ustulina, Xylaria

Plate 209 = Diagnostic Characters -- Pyrenomycetes: Sphaeriales: Chaetomium chamalodes & Neurospora tetrasperma

Plate 210 = Example Structures -- Pyrenomycetes: Sphaeriales: Ceratocystis sp., Ceratocystis ulmi, Daldinia sp., Endothia

parasitica, Hypoxylon sp., Neurospora tetrasperma, Phyllachora sp., Ustulina sp., Xylaria cornu-damae, Xylaria spp.

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The order Pseudosphaeriales is a rapidly growing order, for many forms are being transferred to this group from other areas of the Pyrenomycetes. They are mostly tropical species and ascocarps that are not true perithecia, and thus they are referred to as "perithecia-like" or "ascostroma." They become exposed to the external environment by pushing through the host cuticle. Locules are formed in the stroma and hyphae grow from the top to the base of the locule. They usually persist through maturation and they are called pseudoparaphyses, and no perithecial peridium is formed here.

The ascus wall is uniformly thickened and is actually composed of two layers with no pore at the apex. During release of ascospores the outer wall ruptures and the inner wall balloons-out.

Dibotryon morbosum causes "Black Knot" disease on plum and cherry. The fungus invades the young, elongating shoots of cherry in the spring. The cambial layer of the host is reached by autumn but there is no obvious damage. The mycelium overwinters; and during the second growing season stimulates the cambium of the host to divide rapidly. Also the ray cells are enclarged. This hypertrophy breaks up the cambium. There is also a differentiation of host cells produces a mass that is difficult to distinguish between wood and bark. The mycelium constructs a stroma underneath the hard bark, in the vicinity of the cork cambium. The fungus stroma then ruptures the hard bark of the host.

Many conidia are produced on the surface of the stroma, and there is a Hormodendrum Imperfect Stage in early summer. After the imperfect stage the stroma pushes up a number of papillae on its surface.

Ascogenous hyphae develop in locules of the pipillae and an opening or pseudoostiole forms in the second spring. Asci deliquesce and ascospores are 2-celled being distributed via the psuedoostiolein the locule.

Pyrenophora teres causes "Net Blotch" of barley. Ascostromata are formed and a pseudoostiole allows for the escape of spores. These are muriform, and setae are found on the sides of the ascostroma.

Pleospora sp. are similar to Pyrenospora teres except that there are no setae.

Venturia inaequalis causes the "Apple Scab" disease. Here the mycelium is subcuticular (between the cuticle and the epidermal cells). It does not penetrate the host nor produce haustoria and possesses a curious nutrition that is not fully understood. The mycelium produces a number of upright, unbranched conidiophores; each being terminated by a single conidium. This is the Fusicladium Imperfect Stage (like small candles)

After the conidium is released another forms in its place. The parasitic stage is also the Imperfect Stage here.

The Saprophytic Stage of V. inaequalis occurs on dead material in winter. A stroma forms during winter and the ascogonium is embedded therein a forms a short tricogyne. An antheridium fuses with the tricogyne and its nucleus migrates down a tube to the ascogonium. Although both sex organs are produced on the same thallus, there are compatibility types present. Asci mature by spring and are found in locules in the stroma. Ascospores are 2-celled with one cell larger than the other and they are initiated in the fallen leaves in autumn but do not mature until the following spring. Spores are discharged from the psuedoostiole.

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Please refer to the following plates for characteristic structures and Life Cycles in the Pseudosphaeriales:

Ascomycota: Euascomycetes: Pseudosphaeriales

Plate 139 = Life Cycle -- Mycosphaerella tulipiferae.

Plate 140 = Structures of Guignardia bidwellii.

Plate 141 = Life Cycle -- Venturia inaequalis.

Plate 211 = Life Cycle -- Pyrenomycetes: Pseudosphaeriales: Venturia inaequalis

Plate 212 = Example Structures -- Pyrenomycetes: Pseudosphaeriales: Dibotryon, Pyrenophora, Pleospora, Venturia

Plate 214 = Example Structures #2: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

Plate 215 = Example Structures #3: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

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The order Dothidiales is mainly tropical and has neither paraphyses nor pseudoparaphyses. A locule is digested in the stroma and asci begin to grow in the locule before the latter is mature (unlike Pseudosphaeriales). All asci appear to originate at a point giving a form like a fan at maturity.

Ascospores are released in the same manner as in the Pseudosphaeriales. A pseudoostiole allows for the escape of spores to the external environment. Most species are tropical.

Mycosphaerella sp. has only one locule per stroma. Cymadothea, causing "Clover Sooty Blotch" has more than one locule per stroma and there is a Polythrincium Imperfect Stage. The Perfect Stage matures on overwintered leaves, but is very rare. Dothidea collecta is multiloculate. Ascogonia are embedded in the ascostroma and a locule dissolves around each ascogonium. A pseudoostiole is present.

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Please refer to the following plates for characteristic structures and Life Cycles in the Dothideales:

Ascomycota: Euascomycetes: Dothideales

Plate 138 = Dothideaceous stroma: Typical structure.

Plate 213 = Example Structures -- Pyrenomycetes: Dothidiales, Hemisphaeriales, Laboulbeniales, Hysteriales

Plate 214 = Example Structures #2: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

Plate 215 = Example Structures #3: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

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The order Hemisphaeriales (or Microthyriales) is represented by the Genus Asterina. There are many tropical species. These are leaf parasites that bear a hemispherical ascostromata. The ascocarp is superficial on the host or sometimes subcuticular. The top portion of the stroma is clearly defined and the bottom is a mat of loose hyphae. The asci come to lie beneath a shield-like cover that opens by irregular spitting or may form a pseudoostiole. Pseudoparaphyses may be present.

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Please refer to the following plates for characteristic structures and Life Cycles in the Hemisphaeriales:

Ascomycota: Euascomycetes: Hemisphaeriales

Plate 142 = Structures of Hemisphaeriales: Microthyrium microscopieum.

Plate 213 = Example Structures -- Pyrenomycetes: Dothidiales, Hemisphaeriales, Laboulbeniales, Hysteriales

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The order Laboulbeniales includes nonpathogenic parasites of insects. There are over 100 genera and thousands of species have been described. The species discriminate the site of the insect body they will attack. Many species are extremely minute and are composed of relatively few cells and some species are dioecious. The thallus is non-mycelial and attaches to the host by means of a shield-shaped foot cell with a black pigment at its apex.

Rhizoids have been observed to enter the body of the host. A stalk cell lies on top of the foot cell, which bears a jacket of sterile cells.

Spermatia are produced in the hypha that extends from the stalk cell.

The spermatium joins with a tricogyne and its nucleus fuses with the ascogonium nucleus. A jacket of sterile cells enlarges.

Asci are developed within and generally have four ascospores (others disintegrate). These are forcibly ejected. Male and female fungi generally occur close together on the host, and the ascospores are 2-celled. The larger cell, which is equipped with a sticky substance, goes to the foot cell and the smaller one gives rise to the rest of the thallus.

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Please refer to the following plates for characteristic structures and Life Cycles in the Laboulbeniales.

Ascomycota: Euascomycetes: Laboulbeniales

Plate 127 = Structures of Laboulbenia formicarum.

Plate 213 = Example Structures -- Pyrenomycetes: Dothidiales, Hemisphaeriales, Laboulbeniales, Hysteriales

Plate 214 = Example Structures #2: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

Plate 215 = Example Structures #3: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

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The order Hysteriales forms elongated ascostromata, which are black, hard and carbonaceous. They may be closely packed on wood, giving the appearance of charred wood.

An ostiole opens in an elongated slit called a Hysterothecium. The asci are of the Pseudosphaeriales type and pseudoparaphyses may be present.

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Please refer to the following plates for characteristic structures and Life Cycles in the Hysteriales:

Ascomycota: Euascomycetes: Hysteriales

Plate 143 = Ascocarp & ascus of Hysteriales: Glonium sp.

Plate 213 = Example Structures -- Pyrenomycetes: Dothidiales, Hemisphaeriales, Laboulbeniales, Hysteriales

Plate 214 = Example Structures #2: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

Plate 215 = Example Structures #3: Pyrenomycetes: Pseudosphaeriales, Dothideales, Hemisphaeriales, Laboulbeniales,

Hysteriales.

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The Sub-Class Euascomycetes, Series Discomycetes are the "cup fungi," a group with over 11,000 species. The ascocarp is an apothecium. The hymenium is always exposed and cup-shaped.

There are two Sub-Series: Inoperculatae and Operculatae. The Inoperculatae are mainly parasites that do not have an operculum or "lid" on the ascus. Most species have a conidial stage and the fruiting bodies are quite small. They are usually not coprophilous and the majority produce spermatia. The Operculatae are not usually parasites and they do possess an operculum (boudier).

Most species are without a conidial stage and they usually have large fruiting bodies. A large number are coprophilous and not one produces spermatia. Their ascospores are not elongated.

The Inoperculatae are here represented by two orders: Helotiales and Lecanorales.

The order Helotiales is the larger of the two orders of Inoperculatae. They hve either cup or disc-shaped apothecia with asci only slightly thickened at the apex. The ascospores are round, elliptical or elongated but rarely thread-like. Many of the Helotiales live as soil saprophytes on dead wood or dung or on other organic matter from which they derive nourishment. Some species are very serious parasites on plants, causing various rots of stone fruits and diseases of vegetable crops. Several families and genera will be discussed to represent this order.

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In the family Hypodermataceae both Hypodermella and Lophodermium incite "Needle-Cast Disease" of conifers.

The fruiting body is boat-shaped with a slit down the middle. It shows a resemblance to the ascocarps of the Hysteriales, although it is generally much smaller and less carbonaceous. They are really a transitional group between the Pyrenomycetes and Discomycetes and this fruiting body is like a hysterothecium.

The asci are not double-walled here, a spermatial-type of fertilization occurs and conidia are quite rare.

Rhytisma acerinum causes "Tar Spot Diseases." There is conspicuous black stroma on plants, which is produced close to the surface or directly in the epidermis (= superficial stromata). Ascocarps develop within the stroma and spermatia are produced in the initiation of the sexual process. The ascocarps are in the stroma and radiate out from the center. They stand out as prominent lines on the stroma. The hymenium is broader than in previous forms.

Cryptomyces pteridis is essentially the same as Rhytisma acerinum but is parasitic on bracken fern in North America. There is a conspicuous black stromata. Several elongated apothecia, more or less radiately arranged, develop in each stroma, maturing late in spring on the dead overwintered leaves lying on the ground. The fungus in its parasitic phase has a conspicuous intercellular mycelium with haustoria, and produces large quantities of long, slender, curved spores in acervuli. These break through the epidermis (the Cylindrosporium Imperfect Stage). If the infection is heavy the leaves usually turn yellow and fall off.

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The family Mollisiaceae is represented here by Higginsia hiemalis (Cocomyces), which causes "Cherry Leaf Spot" disease. There is a rapidly developing septate mycelium in intercellular spaces that produce haustoria with long stalks and a bulbous tip. There is a prominent conidial stage.

In the Cylindrosporium Imperfect Stage an aggregation of hyphae forms in a little bed under the epidermis. Conidiophores that are produced on top produce elongated conidia, which are either one- or two-celled or slightly curved.

This mass of protruding conidia breaks the cuticle and is conspicuous (= acervulus).

In the Sexual Stage apothecia form on overwintered leaves on the orchard floor. The sexual process is initiated on the leaves still on the tree but late in the season. Tiny cells are formed at the base of the stroma, which are spermatiophores. They seem to be derived from conidiophores. These produce spermatia.

Down in the leaf there is a massing of hyphae that enlarges (= ascocarp initial). Coiled hyphae are produced on the mass, which develop into a tricogyne, which migrates to the surface. Spermatia attach themselves to the tricogyne.

The stroma enlarges over winter and asci develop. They differ from the Pseudosphaeriales in that there is no double wall and they occur with paraphyses on the hymenium.

Stromatic tissue cracks open like a lid, exposing the hymenium (= apothecium is produced from a stroma the top of which breaks off). Ascospores are straight and never more than 2-celled (remember that conidia may be 2- or 3-celled).

Diplocarpon rosae causes "Black Spot Disease" of rose. Most characters are like Higginsia but the mycelium is subcuticular and not as deep as Higginsia. There is an Actinonema Imperfect Stage. The conidia and ascospores are similar.

Febaea sp. is mostly like Diplocarpon but there is a different Imperfect Stage. The ascocarp may, in a few cases, develop on living tissue of the host.

Mollisia dahnii grows as a parasite on the stems and leaves of Potentilla, a wild rosaceous plant related to the strawberry. The apothecia are matured on the living host.

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The family Helotiaceae is represented here by several genera. Stamnaria americana is of interest as one of the very few fungi that attack horsetails (Equisetum spp.). In autumn numerous apothecia develop and mature on the live stems of the host.. It infects stems and produces ascocarps in autumn on living stems. They possess a rather prominent stalk.

The ascocarp is made up of obviously interwoven hyphae (= prosenchyma). The Mollisiaceae had a stroma, which is a group of very closely oppressed hyphae called a pseudoparenchyma.

Chlorosplenium aeruginosa causes "Green Stain" disease, which is easily observed with the naked eye. It is bluish-green in color and found on oak wood. The green stain is highly prized in Europe. Ascocarps are produced from mid-summer to the end of October. The hyphae contain a green pigment and their color is imparted to the substrate. The apothecia are also green. They are stalked, cup-shaped to funnel-form at the apex where asci are borne, and often asymmetrical.

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In the family Sclerotineaceae apothecia are typically long-stalked with funnel-like tips. They always arise from a slerotium or pseudosclerotium. Most species are parasitic and there is definite spermatial fertilization.

Monilinia fructicola causes "Brown Rot" of stone fruits. This is a highly economically important fungus that attacks fruit at the ripening stage and may develop in transit. The Monilia Imperfect Stage is similar to Neurospora. Apothecia originate from a pseudosclerotium. Tufts of conidia are formed on the host surface, the fruit becoming mummified (it is not a soft rot). The mummy bears the pseudosclerotium. Partially buried mummies on an orchard floor give rise to stalked apothecia. Spores are commonly one-celled and hyaline.

Sclerotinia sp. never has a Monilia Imperfect Stage and apothecia originate from a true sclerotium.

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The family Geoglossaceae are known as the "Earth Tongues." All are saprophytes that grow out of the ground. Apothecia are never cup or saucer-shaped and there is no conidial stage. Instead apothecia are tongue-, cup or spatula-shaped Details of the sexual stage are not well understood..

Geoglossum sp. has a hymenium that spreads on all sides of the apothecium. Ascospores are distinctive.

Leotia lubrica. has a white stalk where the upper portion is convoluted into a dark green cup-like area. The fungal body is very slippery.

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Please refer to the following plates for characteristic structures and Life Cycles in the Helotiales:

Ascomycota: Euascomycetes: Helotiales

Plate 144 = Section thru' Apothecium diagram.

Plate 145 = Life Cycle -- Rhytisma acerinum.

Plate 146 = Life Cycle -- Monilinia fructicola.

Plate 147 = Geoglossaceae structures: Geoglossum ophioglassoides, Spathularia clavata, Leotia gelatinosa & Cudonia circinans.

Plate 216 = Life Cycle -- Discomycetes: Inoperculatae: Helotiales: Hypodermataceae: Rhytisma acerinum

Plate 217 = Diagnostic Characters -- Discomycetes: Inoperculatae: Helotiales: Geoglossaceae, Helotiaceae, Hypodermataceae, Mollisiaceae, Sclerotineaceae

Plate 218 = Example Structures -- Discomycetes: Inoperculatae: Helotiales: Hypodermataceae

Plate 219 = Example Structures -- Discomycetes: Inoperculatae: Helotiales: Helotiaceae, Mollisiaceae

Plate 220 = Example Structures -- Discomycetes: Inoperculatae: Helotiales: Helotiaceae, Sclerotineaceae, Geoglossaceae

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The order Lecanorales includes over 8,000 species, all of which are parasites on algae forming lichen associations. This is considered to be a symbiosis: the alga derives protection from the fungus, which in turn derives nourishment from the alga. In actuality the fungus makes a slave out of the alga = Helotism. Lichens have actually been given binomials. Other fungus groups that together with algae form lichens are in the Pyrenomycetes (about 2,000 species in Sphaeriales & Pseudosphaeriales) and in the Agaricales.

About 18 families have been recognized in the Lecanorales. They are widely distributed in nature from the poles to the tropics. They are especially abundant in the Arctic, where they comprise the principal vegetation, and they are important there for forage of musk oxen and reindeer and have been harvested by humans for their herds. They can live on bare rock; withstand long periods of desiccation, severe cold and severe heat. They do not die in the winter and they may dry down to brittleness, but can reabsorb water.

Classification of Lecanorales is made on the thallus form. Foliose = like a sheet; Fruticose = upright and profusely branched or those that hand from trees, and Crustose = thallus closely oppressed to the substrate. Lichens are anchored to the substrate and they weather the rock (the first step in soil formation). They may break open the rock by sending hyphae into the crevices and acid secreted digests the rock. They are extremely sensitive to noxious gases and are rarely found in urban areas.

The kinds of algae parasitized are unicellular green algae, blue-green algae (Chlorella) and filamentous green algae. Algae may multi80ly by fission when in association with the fungus.

Parmelia sp. forms a compact layer of interwoven hyphae on two sides (= pseudoepidermal layer). A loose system of hyphal threads extends between these. Rhizines are produced at the base, which serve for anchorage and absorption of some water and minerals from the substrates. The algae occur near the surface surrounded by a loose mass of hyphae (they are always embedded in the fungus thallus). The alga is protected from direct rays of the sun as the fungal covering produces the blue-green color of lichen. This also lowers the risk of desiccation. Hyphae derive food from the alga in two ways: (1) by hyphal contact and (2) by small haustoria.

Propagation of the fungus usually occurs by braking off of a portion of the thallus through the agency of wind, etc. This process is known as Multiplication by Fragmentation. A soredium occurs where several algae are suspended by some fungal hyphae above the pseudoepidermal layer.

During ascospore formation an ascogonium that is produced down in the hyphal mass, which sends up a tricogyne.

A spermogonium is produced with an ostiole protruding from the pseudoepidermal layer.

After the spermatia attach to the tricogynes, the male nucleus migrates down the tube of the tricogyne and fuses with the female nucleus in the ascogonium. Ascogenous hyphae form croziers and these produce asci. In the meantime the apothecium is formed around the ascogonium. Ascospores are forcibly discharged. Apothecia form on the surface, and algae may or may not be carried along into the ascocarp.

Ascospores will not germinate unless they alight on a specific alga, which is one in a million!

Lichens are an extremely important group of organisms. They colonize barren lands and serve as forage for animals. They may supply food for humans in emergencies, but most are toxic and boiling or leaching is required. They have been used in the production of purple dyes and in the perfume industry. They can cause extensive damage to stained glass windows in cathedrals and indirect damage to trees by harboring insects.

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Please refer to the following plates for characteristic structures in the Lecanorales:

Ascomycota: Euascomycetes: Lecanorales

Plate 221 = Example Structures -- Discomycetes: Inoperculatae: Lecanorales

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The order Pezizales and two families Pezizaceae and Helvellaceae here represent the Operculatae. Almost all Operculatae are saprophytes on dead wood, leaves, dung, etc. They have an operculum or lid on the ascus, and very few forms produce conidia. Fruiting bodies are considerably larger than the Inoperculatae. There are no spermatia. Ascospores are one-celled, never markedly elongated and often ornately sculptured.

The order Pezizales may have cup or saucer-shaped apothecia and stalked apothecia depending on the family.

The family Pezizaceae or cup fungi is represented here by several genera with different characteristics. It is a relatively large group of saprophytic forms that grow on old wood, rich soil, dung, etc. Their apothecia are typically cup-shaped or discoid, and may be stalked or sessile. There is a wide range in size, color and other details. Some species are heterothallic. The Genus Peziza has an apothecium that may be one foot in diameter. The Genus Aleuria has reticulate sculpturing on the ascospores. The Genus Urnula is the earliest to appear of the fleshy fungi in North America. They always occur on buried wood and they have black spores and ascocarps.

Paxina and Plectania have a well-developed stalk and diagramatic cup. Ascobolus has many coprophilous species. Apothecia are quite thick and have purple spores.

Pyronema grows where soil has been heated, e.g., around old campfire sites, in greenhouses, after a forest fire, etc.

Sexual Reproduction in The Operculatae

Many forms in the Pezizaceae have been studied, but not a single member in the whole order produces spermatia. An example is Pyronema where there is development of branches from certain hyphae that are swollen at the tip and delimited by a cross-wall. Many nuclei pass from the antheridium into the ascogonium. The nuclei then pair in the ascogonium.

Paired nuclei move out into ascogenous hyphae.

At the same time that ascogenous hyphae are produced, sterile hyphe and paraphyses grow from beneath the ascogonium. Thus the stalk and excipulum are formed.

Another example is Ascobolus that contains a considerable number of coprophilous species. They have small apothecia, 1-2 mm. in diameter. Ascospores are large with purple spores. During sexual reproduction the ascogonium occurs with an antheridium. These ascogonia may be coiled and tapered. Ascogenous hyphae form from the coil after fertilization.

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The family Helvellaceae is the saddle fungi all of which are saprophytes. The apothecium is always stalked and never cup-like. The Genus Helvella has the following saddle shape:

The Genus Morchella has a hymenium that lines all the depressions. All are edible and highly prized. The mycelium persists in the ground from year to year.

In the Genus Verpa, the ascospores vary from globular to elliptical, but never elongated nor mullticellular. Spores may be sculptured (a condition is essentially nonexistent in the Inoperculatae).

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Please refer to the following plates for characteristic structures in the Pezizales:

Ascomycota: Euascomycetes: Pezizales

Plate 148 = Ascocarp & ascus: Elvella crispa.

Plate 222 = Example Structures -- Discomycetes: Operculatae: Pezizales & Tuberales

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The order Tuberales includes the truffles, which are highly prized for their flavor. There are more than 200 known species of which about 62 have been found in America, mainly in California. The fruiting bodies are mostly subterranean, and those of certain species in the genus Tuber are the most highly prized. The fruiting bodies are mostly closed structures and do not resemble apothecia. Most species do not have an ascal opening. The ascocarps range in size from smaller than a pea to several centimeters in diameter. They are somewhat globose, often fleshy structures with a smooth or irregular surface. The asci line one or more chambers, which open to the outside; or the ascocarp may be essentially solid, closed and indehiscent, its asci appearing to be scattered and imbedded in sterile tissue. The fructification of the Tuberales has been interpreted as a modified apothecium, and this has directed its classification into the discomycete group and close to the Pezizaceae.

The Genus Tuber has mycorhizal forms on oak roots. They occur all over the world, but are commercially harvested in France, Italy and Spain. They are also common along the West Coast of North America. Truffle hunters use dogs and pigs to hunt down the fungi, which are buried several inches below the ground. Ascocarps may be up to two inches in diameter. Veins separate the globular scattered asci. This is actually a very highly evolved apothecium. The cup is convoluted into a system of folds in evolution; asci are typically operculate. Asci are also globular and the spores are sculptured, 1-celled and short. Typically there are 2-5 spores per ascus.

The Genus Genea is more primitive than Tuber and contains a small ostiole.

The Genus Pseudobasamia causes "Calves Brains Disease." The apothecium is quite small (1/2 the size of a pea), and it is produced in convoluted masses. These are pests of the mushroom industry as they inhibit the growth of commercial varieties.

Spores of the Tuberales are generally distributed by animals, which dig them up for nourishment, the spores then passing through the alimentary tract.

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Please refer to the following plates for characteristic structures in the Tuberales:

Ascomycota: Euascomycetes: Tuberales

Plate 149 = Tuberales ascocarps: Tuber aestivum, T. rufum & Genea harknessis.

Plate 222 = Example Structures -- Discomycetes: Operculatae: Pezizales & Tuberales

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Bibliography

◄Introduction Higher Fungi ►

True Fungi (Eumycophyta1

Ascomycota (Ascomycetes, Ascomycotina) -- Sac fungi

True Fungi (Eumycophyta¹