An introduction to poroide fungi
2. Macromorphology
Vegetative and reproductive stages
In contrast to most agarics where basidiocarps develop (in part) in soil and the last stage is more or less a matter of tremendous expansion, basidiocarp development among polypores is preceded by a visible vegetative stage.
Inside the substrate there is usually a vast network of hyphae from which a mycelial mat may emerge onto the surface of the substrate and from which the mature basidiocarp develops, often after a considerable span of time. Such sterile mats are frequently collected, especially with resupinate polypores, and they should normally be discarded.
In other cases a sterile ‘knob‑like’ stage may be found, which may sometimes be correctly identified because of its structure, colour, scent etc. However, such collections will normally be of restricted value. Distinct asexual (anamorphic) stages are rather rare among the polypores (see Ryvarden 1991 for a full list). In some cases they are completely separate from the sexual (teleomorphic) stage e.g as seen in Ptychogaster aurantiacus or Laetiporus sulphureus.
Most often, both asexual and sexual stages can be found together as, for instance, in Oligoporus ptychogaster where the former develops earlier than the latter. In such a case a reliable identification can be reached. However, the classification and keys used in this manual are based on the sexual reproductive stage.
Types of basidiocarp
Some polypores are rather variable with regard to basidiocarp characteristics, but for most the shape, attachment, colours, etc., are stable and distinct and are important characters.
The most common types of basidiocarps are shown on fig.1. However, it is important to note that in some species development from resupinate to effused reflexed basidiocarps occur, or that in some, both resupinate and distinctly pileate basidiocarps may occur on the same log or stump.
Thus, it is necessary to use the terms with discretion and understanding. Besides the type of basidiocarp, the attachment to the substrate may also be rather distinctive. A pileate basidiocarp may, for example, be broadly sessile or may taper at the base almost to a stipe. Again there will be transitions in some species while others are rather consistent.
Consistency
With some experience it is often possible in the field to tell something about the hyphal structure from the consistency of fresh basidiocarps. Perennial basidiocarps with a dominance of skeletal hyphae will normally be woody, while trimitic ones will be tough and difficult to tear apart. Monomitic ones may be soft or very sappy and may shrink considerably during drying, often accompanied by a colour change.
Scent and taste
Most polypores have no distinct taste or scent, but some e.g. Haploporus odorus, Trametes suaveolens and Gloeophyllum odoratum have very distinct scents. Such a character should be recorded as it has a tendency to disappear on drying or storing. No polypores are poisonous as far as we know, but many have a bitter taste.
There are few edible polypores, species of Albatrellus being the most popular. In North America it is traditional to collect and eat Laetiporus sulphureus, but this habit is not common in Europe as specimens may be toxic. Other species eaten from time to time include Meripilus giganteus, Grifola frondosa, and Fistulina hepatica. In Japan there is a large industry based on cultivation of Meripilus giganteus and Grifola frondosa and dried specimens of these species can be purchased in supermarkets.
Fig. 2. Sections of different basidiocarps a) perennial with mycelial core and distinct annual layers in the tube layer, b) stipitate annual, c) effused reflexed, d) resupinate nodulose, e) resupinate annual, f) resupinate perennial with distinct tube layers, g) basidiocarp with zones and umbo, h) perennial basidiocarp with annual tube layers, i) homogenous context, j) duplex context, k) duplex context with dark zone. Del. T. Niemelä.
Consistency
With some experience it is often possible in the field to tell something about the hyphal structure from the consistency of fresh basidiocarps. Perennial basidiocarps with a dominance of skeletal hyphae will normally be woody, while trimitic ones will be tough and difficult to tear apart. Monomitic ones may be soft or very sappy and may shrink considerably during drying, often accompanied by a colour change.
Pileus surface.
In many species the pileus has a distinct colour which remains reasonably unchanged through the life span of the basidiocarp. This is true for many species with brown‑coloured tissue.
The colour apparently is due to complex polyphenols, these highly resistant to degradation by natural causes. In other species the colour may fade because pigments in the upper layer have been destroyed by weathering. Trametes cinnabarinus, a species with brilliant reddish basidiocarps, is an excellent example of this.
White and light coloured species often become darker with age as the upper layer of hyphae collapses and becomes darker, usually in ochraceous to brownish shades, resulting in a distinct zonation from the base to the margin where new hyphae are actively developing.
This is typical in perennial basidiocarps, and (for instance) in Phellinus it is common to see blackish basidiocarps with a whitish to pale yellowish margin in which the hyphae are still thin walled and almost hyaline, whilst in the basal part they will be solid, dark coloured and agglutinated to a virtually indestructible mass.
In some species with normally light coloured basidiocarps, a thin, black or deep reddish cuticle may develop from the base, making the pileus strikingly bi‑coloured. A section will reveal that the coloured layer is very thin. Such a cuticle is of little taxonomic significance as one may often find specimens with and without such a layer in a large collection.
The pileus surface may be glabrous or covered with hairs of different types. When glabrous the surface may be dull or shiny and, in some cases, with a distinct cuticle. In most cases such a cuticle will have no special structure, while in other species, as in many Ganoderma species, it may be very distinct and consists of a dense palisade of club like hyphal endings.
A glabrous pileus may be smooth without any zonation, radial lines or raised ridges. However, it is often common to see a distinct sulcate zonation reflecting different stages of growth, commonly combined with some radial lines or raised edges. The latter may become more prominent on drying as basidiocarps of many polypores have a tendency to shrink slightly when dried.
For some species the pileus cover may have a distinct character although it may be difficult to describe it properly. The reason is that such hairs, which normally are composed of hyphae, have a variable development according to weather conditions. In wet weather the hyphae are seemingly shorter and more agglutinated than in dry weather. The type and consistency of the pileus cover however, plays an important taxonomic role and varies from velutinate via tomentose to hispid.
Basidiocarps of some species with hairs on the pileus are long lived or perennial and often algae become established between the hairs, giving the pileus a greenish shade. In other species the hairs may erode with age or become agglutinated to the surface as warts, or lines of scrupose tufts of hyphae, as seen in Gloeophyllum sepiarium.
In some species there is a distinct, dark, cuticle below a tomentum and with age, the hairs may fall off, often zone wise, exposing the
cuticle which then contrasts strongly with the lighter coloured tomentum. A good example is Trametes versicolor where the number of zones and their colour may vary tremendously.
In many perennial species the pileus may crack with age, either forming radial lines or an irregular pattern of angular pieces, often so strongly and characteristically that the surface is referred to as rimose.
Margin
The margin and its development, especially in species with resupinate basidiocarps, may be an important character.
Some species have a more or less even sterile margin one to several mm wide, often white or light coloured. The hyphae grow at an equal rate causing the margin (especially obvious under a lens) to becomes soft and finely tomentose.
However, there are species where strands of hyphae (mycelial cords) are developed, often in a particular way. Such a character will normally be important. In other species the margin may end abruptly with an almost vertical slope. Such basidiocarps often have a tendency to curl up and loosen along the margin on drying.
Stipe
The attachment of the stipe to the pileus is shown in fig.1. The consistency and colour of the stipe will normally be that of the pileus. However, in a restricted number of species the stipe may be differently coloured, such as in several Polyporus species where the stipe is darker than the pilei. The tubes may be more or less decurrent on the stipe, especially when the stipe is expanding upwards and the whole basidiocarp has a conical shape. In other cases, as in many species of Polyporus, the stipe has the same width from base to pileus.
Some species have an applanate basidiocarp that is so strongly fan-shaped or tapering towards the base that it may be difficult to decide whether a true lateral stipe is present or not. In such cases only experience will help, but if there is a distinctly non poroid area on the lower side of the base, close to the attachment, it is a good indication that a lateral stipe is present.
In a few species more than one pileus may develop from a common stipe or elongated base. In such cases pilei will be fan shaped and will overlap at the circumference of the basidiocarp. Circular pilei are found (very rarely) in species such as Polyporus umbellatus which produces many pilei from a common stipe.
Sclerotia
A very few polypores develop an underground sclerotium consisting of a dense mass of hyphae. In some these may enclose soil or small rocks and stones.
Very often the collector is not aware of the sclerotium as it is deeply buried in the ground, as is the case with some Polyporus species.
Fig. 3. Schematic drawings of different types of pores, a) Entire margin on resupinate basidiocarp, b) rhizomorphic margin, c) no distinct margin, d) round pores, e) angular pores, f) radially elongated pores, g) deadaleoid or sinuous pores, h) gilled pores, i) receding pore surface. Del T. Niemelä.
Pore surface
The colour of the pore surface is characteristic and diagnostic for many species. With age it has a tendency to become darker and this has to be remembered when using keys.
More important than the colour is the shape of the pores and their size. For most species the number of pores per mm or cm is rather consistent although the pores often have a tendency to become larger with age and in large specimens. However, there are exceptions to the round or angular pores and fig. 3 shows some important types of hymenophore.
While some species have consistently poroid basidiocarps, there are a few confusing ones such as Trametes elegans and Daedaleopsis confragosa where the hymenophore may change with age and development. In these species poroid specimens have been found side by side with lamellate ones and even single basidiocarps may be poroid and lamellate in different parts, indicating that configuration of the hymenophore may not be so strongly genetically fixed as often assumed.
With age the pore mouths (dissepiments) in some species may be incised or become dentate as they develop at different rates. In such cases it is normally easy to observe that the basal parts of the tubes are coherent and that we are confronted with a polypore and not a true hydnoid species.
However, there are cases, such as in Schizopora paradoxa where this may be difficult to see as the tubes may be split to the very base. In these the resultant spines are often somewhat irregular, flattened and of unequal length from the margin towards the central part of the basidiocarp. A small number of such species are included in this manual because we are convinced, with evidence from their hyphal structure, that they belong among the polypores more than with hydnoid fungi as seen in Thelephoraceae and Corticiaceae s. lato.
The pores or lamellae are indicated as a certain number per mm or cm. This measurement has to be taken tangentially to the margin as many pores have a tendency to be elongated radially by age. It is important to take measurements in several places to avoid atypical development. It may be convenient to cut a mm‑paper in small bits and place a piece on the pore surface and count through the lens.
It is important to observe that the number of pores per mm does not automatically indicate how easily the pores are observed. In some perennial species the dissepiments are so thick that even if the pores are only 4‑5 per mm, they are almost invisible to the naked eye, whilst in species with thin dissepiments there may be 7‑10 pores per mm with the same pore size.
Tubes and context
In most species the tubes are more or less concolorous with the pore surface but with age may become paler than the pore surface and in these there is no apparent difference either in colour or consistency between the tubes and the context or subiculum.
However, in other species the tubes may have a another colour, consistency and even hyphal system than the context. These differences may be important taxonomic characters, and a specimen should therefore always be sectioned to observe the tubes and context. In some genera such as Gloeoporus, there may also be a distinct zone or dense layer between the tubes and the context.
The context is the sterile part of a basidiocarp between the tubes and the pileal surface. In resupinate basidiocarps the sterile part between the tubes and the substrate is often called the subiculum although there is no significant difference between these two types of tissue.
In most species the context is homogeneous regarding both colour and consistency and will normally have a radial structure as the hyphae grow from the base towards the margin. However, in some the context is distinctly duplex, the lower part dense and without apparent structural directions while the upper part is more soft and fibrous, often intergrading with a tomentum on the pileus surface.
In genera like Datronia and Trametes many species have a black zone between a lower dense context and an upper loose context or a pileus tomentum. Such a zone is always best developed at the base and may be an important and reliable character.
In some species with duplex consistency the tomentum and lower context may have different hyphal constructions, and binding hyphae will normally never be present in the tomentum.