The North American Species of Pholiota
In Pholiota, the gross features of the basidiocarp—the pileus, flesh (context), lamellae, and stipe—are now as important in taxonomy as they were in the Friesian era. An analysis of the details relative to each structure gives some indication of their use in taxonomy.
Pileus. In our experience, the colors and surface characters of the pileus are highly important in the identification of species. On the other hand, the size, shape, habit of growth, and habitat are of lesser value, and are merely supplemental to those of color and surface features.
In general, the predominant colors of the pileus are in the yellow and brown series. In a relatively few species, there are red tints which modify the browns and yellows. Grays and general lack of pigmentation are present in some, but species with permanent pure white pilei have not been encountered. The pileus is whitish in P. destruens, but it develops colors toward maturity, and in P. lutescens the pileus is at first white but gradually becomes lemon-yellow. A common color pattern is that the central portion of the pileus is darker than that of the marginal area; the disc may be brownish, and the marginal area buff to yellowish. Often the colors are of darker tints in the "button" stage than at maturity. A rare color-display is found in P. polychroa; the surface of the pileus is of many colors-purplish when young, then changing to buff or yellowish, or often to olive to greenish on the marginal area, the disc remaining more or less purplish or becoming yellow to orange. Colors and color patterns are valuable in distinguishing species.
Surface modifications are, in many species, noteworthy, and their character should be determined. The pileus surface may be glabrous; or, in other species, it may be fibrillose, and the fibrils may be aggregated into scales. Pronounced development of scales is striking in the subgenus Pholiota; see P. squarrosa, P. squarrosoides, P. terrestris, and others.
It is important to determine whether the fresh pileus is dry or viscid. When truly viscid, the surface will display a zone of gelatinized hyphae when sections of the pileus are mounted in KOH. In doubtful cases final decision as to whether a pileus is viscid must rest on such a microscopic examination. In a high degree of gelatinization, the pileus surface is glutinous or slimy when wet.
The diameter of the pileus may vary, with the species, from 10 mm or less to 10-20 cm. In a large number of species the pileus is 2-5 cm broad. Pileus shape tends to be convex then becoming more or less expanded. In some species it is umbonate, and in a few the disc may be depressed. Size and shape, however, are usually of relatively minor value in taxonomy. The basidiocarps, in some species, are caespitose; in other species they may be scattered or solitary on the substratum. Their habit of growth varies with the species, but these characters are likewise of somewhat limited taxonomic value since field observations indicate that here the supply of available food is an important factor.
Species of Pholiota are found growing on soil, wood, or humus. Some seem restricted in their habitat; for example, a few species, such as P. highlandensis and P. carbonaria, grow on burned areas around charcoal. In P. sphagnicola, the basidiocarps grow among sphagnum—a rather specialized habitat. A few wood-inhabiting species seem to be confined to either hardwood or coniferous wood; but others are found on both. Habitat in itself is usually of secondary importance in critical identification.
In this study we have made no use of the hygrophanous or non-hygrophanous character of the flesh. We have not seen every species in the fresh state, and for many species records of this character are not available. For those studied too often the caps are "subhygrophanous" indicating at best a state not too valuable as a taxonomic character. However, there are exceptions.
Context. The color, odor, and taste of the pileus context (flesh) should be noted in fresh material.
Color is constant enough to be of value at the species level. The flesh may be yellowish, more rarely brownish, or often white or pallid. In P. avellaneifolia the flesh of the pileus is white, but when cut it slowly becomes pinkish buff. Other color changes taking place on injury to the context will be found in the text. In many species the color may be white to pallid at first but in old specimens becomes distinctly yellow. This makes it difficult to use the color of the context as a taxonomic character because weather conditions as well as age seem to influence this change. Also, in sterile or semisterile basidiocarps, there is often a decided development of yellowish pigment—to the confusion of the taxonomist.
Odor is, in many species, not distinctive. However, in a few it is both noticeable and distinctive, and should be recorded. Odors described for the various species are fragrant (in P. humii, rubronigra, stratosa, subvelutina, scamba); or in P. melliodora, of honey; in a very few species the odor is of coal-tar (P. graveolens); rarely is it raphanoid (in P. vernalis); and in P. squarrosa some collections have an odor of garlic. The odor of freshly unhusked green corn is noticed in some collections of subgenus Flammuloides. In view of the present emphasis on "chemical characters" in the fungi it must be kept in mind that both taste and odor are based on particular chemicals and hence may be as important as, for instance the color change with iron salts.
Taste, like odor, is not distinctive in great numbers of species. It is bitter in P. astragalina, gregariiformis, alnicola, multifolia, and in P. scabella it is described as bitter-acrid. Taste is mawkish (a term used by Murrill) in P. hypholomoides, of radish in P. schraderi, subalkaline in P. flavida, and nutty in P. angustifolia, johnsoniana, and oregonensis. A characteristic odor and taste are rarely similar to each other, but both are farinaceous in P. harenosa, and raphanoid in P. fulvosquamosa.
In summary, color of the context is an important macroscopic character but one subject to certain confusing variations. Odor and taste may be only of confirming or supplemental value, but deserve more study.
Lamellae. A significant character of the gills is their color in the young stage. At maturity, the color is in the yellow-brown to rusty series and is then of little or no value in distinguishing species. The gills may be pallid when very young but soon become some shade of yellow or in some species avellaneous. Occasionally, one encounters a species in which the gills become stained when bruised or in age (P. aurantiobrunnea, mutltifolia). Gill width and spacing may be of some importance when in extremes (distant or crowded, very broad or very narrow). In P. multifolia, for example, they are noticeably crowded and narrow—characters which aid in field identification of this species. Gill attachment offers little assistance in an effort to separate species of Pholiota. The typical condition when young is adnate and in age adnexed or somewhat decurrent.
Stipe. We have customarily recorded the stipe dimensions in our descriptions, but, only in rare and extreme instances is stipe-length of value. In P. malicola var. macropoda, the stipe measures 10-18 cm long and 10-25 mm thick—whence the varietal name. However, in addition to this obvious character, there are other distinctive features. Stipe width is a much better index for species recognition, but a great majority have stipes 5-15 mm diam. However, a few species exhibit very slender, short, delicate stipes.
Surface characteristics of the stipe are important and are to be noted. In one species, the stipe may be glabrous, in another fibrillose or scaly. Usually the veil remnants and cuticular hyphae are dry, but in P. adiposa the scales are notably gelatinous. Stipe color should be observed; in many species the stipe is more or less concolorous with the pileus. In others, the apical and basal portions may differ markedly from each other since the base of the stipe often darkens. It should be determined whether the stipe darkens, with maturation, from the base up, or is rusty brown from the very beginning.
Inner Veil. As the basidiocarp reaches maturity, there are present] in most species, remnants of an inner veil, or cortina, as a ring on the upper portion of the stipe. This ring of fibrils is commonly brownish from spores which have lodged on them. The ring or zone of veil-remnants is usually inconspicuous and often evanescent. Its color (often either white or yellow) in the early stages of the basidiocarp should be noted. When strongly developed, the veil may be membranous and persistent, as in P. albivelata. In one species, P. velaglutinosa, the elements are gelatinous, and the veil is described as glutinous. In other species, the veil breaks so that remnants cling to the margin of the pileus, a condition described as appendiculate. Finally it appears that in some species the inner veil is absent. In P. nigripes for example, no trace of such a veil was found, even in young basidiocarps. With the exception of the glutinous veil, and the veil which forms a membranous persistent annulus, the color of the inner veil is its most valuable feature for taxonomic emphasis.
Outer veil. The development of the veils was studied by Sawyer (1917) for P. adiposa and P. flammans. It is now apparent that the species he studied were P. squarroso-adiposa and P. flammans. The outer veil, or blematogen as he used the term, may be regarded as part of the ground tissue within which the active differentiation of the basidiocarp occurs, and the amount to which this layer develops varies with the species. In such species as P. squarrosa this layer continues to grow along with the differentiating basidiocarp to the point that at maturity conspicuous aggregations of its hyphae persist as scales. As Sawyer pointed out the hyphal arrangement in the blematogen tissue is at first perpendicular to the developing cap surface. Hence as these hyphae elongate they become decumbent and by the expansion of the cap become aggregated into separate fascicles oriented toward the cap margin away from the disc, but often standing straight up (squarrose) on the disc. These scales are innate (firmly attached to the pileus). At maturity they appear to be a direct outgrowth from the pileus. When the gelatinous layer forms underneath them however, there is no solid connection to the cap and they can be easily washed away by rains. It is difficult in Pholiota to distinguish at all times between a partial and an outer veil as in most cases over the stipe the two tissues appear grown together and the fibrils assigned to each are better identified by their position on the stipe. As already pointed out those of the inner veil leave the zone nearest the apex of the stipe. Veil material left on the stipe below this is likely to be mostly outer veil material. For the species without well developed scales on the pileus it must be recognized that the development of the outer veil is reduced. In the subgenus Pholiota, in keeping with the derivation of the name, the central feature is the presence of numerous scales on the pileus and these scales are to be interpreted as remains of the blematogen. However, the structure of the scales themselves is important taxonomically. In some the end-cells of the hyphae may be somewhat cystidioid, in some the hyphal walls may be slightly thickened, colored or encrusted, etc.
In summary, the more important taxonomic macroscopic characters in Pholiota are color and surface features of the pileus, color of pileus context, color of the gills and the surface characters of the stipe. The texture of the inner veil becomes a valuable character when it forms a persistent, membranous annulus, or leaves copious remnants. Finally, the color of the inner veil when young is regarded here as of some value in distinguishing species.
In the present study and in line with the hyphal approach to the study of the basidiocarp, we have placed emphasis on hyphal end-cells, whether occurring as pileo- caulo- pleuro- or cheilo- cystidia, the types of hyphae making up the various tissues, and hyphal detail in the veil in so far as the available material allowed this. The spores, of course, were studied on a modern basis with due emphasis on wall features as well as size and shape. The features offering the most value for taxonomy appear to us to be spore size, spore shape, presence or absence of pleurocystidia and if present their type, the structure of the pileus cuticle, the presence or absence of caulocystidia and whether the hyphae of the subhymenium gelatinize or not.
Spores. We have examined spores mounted in 2% KOH and in Melzer's reagent when studying dried material. Water and 2% KOH are now both regularly used on fresh material. The spores under a good oil immersion lens when viewed individually free from the tissues of the basidiocarp appear ochraceous to ochraceous tawny, tawny or some shape of pale to dark cinnamon. Whenever possible spores from deposits were examined; however for most collections including many of the types, deposits of spores were not available. Under these circumstances we checked the spores found on the apex of the stipe while in the process of looking for caulocystidia. We did not find enough caulohymenium in the species studied to create a situation similar to that found by bolete investigators in Leccinum where there is a fairly extensive caulohymenium at times and the spores produced on its basidia are very different in size and shape from those on the basidia of the hymenophore.
Spore deposits should be taken on white paper and air-dried or dried over silica gel before the color is recorded. There is a characteristic range in color, or color spectrum, for the genus. In this respect Pholiota is like other large genera such as Psathyrella, Coprinus, Russula, etc. The central color is a dull rusty brown to cinnamon brown and there are variations to reddish, earth brown or paler to ochraceous or clay-color to olive-yellow (in P. olivaceodisca). We believe that by using standardized spore prints by the drying methods suggested here, more can be done with the color of the spore deposit as a taxonomic character at the infrageneric level than we have done. We simply do not have the necessary data at this time. We do know, for instance, that in some species such as P. polychroa the spores are quite dark when moist, but we do not have properly dried spores for comparisons. One of the major problems still to be resolved in relation to Pholiota and the Geophila group of genera (Psilocybe, Naematoloma and Stropharia) demands critical observations on the color of the spore deposits, since this is at present the only major distinction between the two groups.
The spore wall for the genus is smooth by definition, but two species are admitted in which one can find irregularities on the surface of some of the spores (e.g. P. aurea). In thickness the wall ranges from less than 0.25 µ to 0.5 µ for the majority of the species, but in a number it is from 0.5-1.5, µ thick. The apical end is typically furnished with a germ pore, but in most species it is not broad enough to affect the outline of the spore apex as seen in optical section. In a relatively small number of species the spore apex appears somewhat truncate to distinctly truncate because of the width of the pore. It is the small-spored species of this group that Singer and Smith at one time segregated as the genus Kuehneromyces. However, we have found all degrees of the development of the germ pore from a broad one causing the apex of the spore to appear truncate to one so small it could hardly be discerned with a 1.4 NA oil immersion lens. On the basis of the material we have examined the truncate spore apex does not correlate well enough with other features of the basidiocarp to justify a group at the rank of genus or subgenus. This was a surprise to us, as it may be to others. We have found on some specimens that the pore, on spores from four-spored basidia is small and does not change the configuration of the spore apex, but on larger spores from 2-spored basidia the pore was larger and in some the apex could be termed truncate. As we see it, the important feature is the presence of the pore, not its width. Singer's (1963, p. 549) statement "... always with a broad truncate germ pore" simply does not hold up if you look at the spores. We might add that it is the spore which is truncate at the apex, not the germ pore. Singer's statement should be read this way.
When viewed from the front (face view), spores in Pholiota are usually elliptic. In the same mount, however, a species may exhibit a range in form from elliptic to ovate or subovate with one or the other usually dominating. In a large number of species the shape in face view is rather monotonously elliptic, with a smaller percentage in a field being subovate. In such instances little use can be made of spore-shape in the taxonomy of the genus. On the other hand, a few notable exceptions occur as in P. pulchella, in which the spores in optical section in face view are distinctly ovate to broadly subfusoid. They are also rather thick walled. In side-view (profile), it is common, in large numbers of species, to find that the spores are inequilateral to some degree, or vary in a different pattern to phaseoliform (bean-shaped). In our descriptions we have tried to indicate the degree to which the spore is inequilateral by the use of three terms: obscurely, somewhat and simply inequilateral. In an obscurely inequilateral spore in profile the ventral line in optical section is humped slightly on the side toward the apex—if one were to make a medial transverse section of the spore. The dorsal line, however, is "humped" slightly back of this medial section or about at the medial position, but in a transverse line across the spore the two humps do not coincide at their peaks. The degree to which the suprahilar plage is depressed will then be the factor most important in determining the category: if slightly depressed the spore is said to be somewhat inequilateral. If not or scarcely at all depressed the term obscurely inequilateral is used. If the suprahilar depression is distinct and the spore is drawn out to a more or less narrowed apex the unqualified term inequilateral applies. The term bean-shaped or phaseoliform means exactly what it says: the profile of a navy bean.
Spores in Pholiota vary with the species from small (3.5-5 x 2.5-3 µ) in P. flammans, to relatively large in P. albocrenulata (10-14-18 X 5.5 -7-8 µ). In the bulk of the species, however, the spores fall in a range in length of 6-9 μ. In subgenus Flammuloides this is particularly true; there is one group of about fifty species in which they measure 5-7.5 X 3.5-4.5 μ.
Although reactions of the spore wall with iodine (Melzer's solution) have not been emphasized greatly in the study of brown spored agarics, we have found a group of species (subgenus Flammula) in which the spores are a darker reddish brown in it than when revived in KOH-in other words they are somewhat dextrinoid. This feature correlates so well with absence of pleurocystidia and bright yellow pilei that it is used as a major feature in redefining the subgenus. In P. brunneidisca a few spores show a violet-brown coagulated content in Melzer's reagent.
Basidia. These structures are normally clavate and 4-spored, and are of such uniformity in Pholiota that their importance in taxonomy as morphological structures showing differences is minor indeed. It is true that in some species they are relatively large, up to 40 X 10 µ, but most often they are 22-28 X 5-6 µ or smaller. In some species both 2- and 4-spored basidia were found, but none were consistently 2-spored only. At times the content of the cell may be brown in KOH, but this is not a constant feature of the type that can be used in species recognition. However, it is of theoretical interest in that in this genus some hyphae and their end-cells can serve as a container for certain compounds and still perform such basic functions as producing spores. More will be said of this feature under the heading of gloeocystidia.
Pleurocystidia. Sterile end-cells interspersed among the basidia in the hymenium are common and often conspicuous. In form, one encounters two general types: 1) those which project conspicuously beyond the hymenium, and 2) those which are more or less buried in it and project only slightly or not at all.
1. The projecting type. The term Flammula-type is no longer appropriate for this type as a name since the type species of Flammula does not have pleurocystidia. In shape this type is basically fusoid-ventricose. There is a long narrow pedicel, a broad submedial enlargement and a long often tapered neck ending in an obtuse to subacute apex. In many species the wall is uniformly rather thin, but in some the wall is obviously thickened at least over the ventricose region. In the following account the dividing line between "thick" and "thin" is at 0.5 μ. In some species less than half the cystidia will show a thickened wall. In others nearly all the cystidia will have walls 1.5-3 µ thick. There is an interesting problem here in the nature of the cell wall which needs critical study. We have used this wall feature as a sectional character in Flammuloides in order to focus attention upon it.
In some species the neck is more or less of equal diameter but in others it tapers gradually outward to the apex. In P. macrocystis the neck is rather uniformly constricted at its base. The apex, in a few species, may be encrusted and varies from acute to obtuse or broadly rounded. The content of these cystidia is of some interest. As revived in KOH many are found to have a homogeneous plug of yellow material which more or less fills the neck and may fill or nearly fill the ventricose portion also. Since chrysocystidia are described by some authors as having a yellow content in ammonia, or becoming differently colored with other dyes, the question as to whether these large cystidia are leptocystidia (which are said to lack distinctive content), or gloeocystidia of the type called chrysocystidia, is worth some thought. A discussion of this point is included under chrysocystidia. We have used the presence of these large pleurocystidia as the major feature of subgenus Flammuloides.
2. Chrysocystidia. In subgenus Hemipholiota as well as in section Pholiota, pleurocystidia of a kind different from the Flammuloides type are encountered. In general, these are non-projecting, clavate, often with an apical short protuberance, and often with an amorphous yellowish content in the enlarged portion as revived in weak bases such as KOH. Not infrequently the amorphous content is present only in some of the cystidia as seen in a given gill section, the others having a hyaline homogeneous content. This type of pleurocystidium (with the amorphous content) is termed a chrysocystidium if it has the refractive content or inclusion as revived in KOH. Their presence is used here as one of the features for distinguishing subgenus Pholiota. Accompanying these, one also often encounters pleurocystidia which are more or less clavate and at the same level as the basidia in the hymenium, but in contrast to the true chrysocystidia, their contents are partially or wholly brown. Since all these types of buried to very slightly projecting pleurocystidia are of about the same type and size, they have here been used to group together the species showing them. It should be understood that we recognize this collection of sterile end-cells as colored basidioles, true chrysocystidia and small leptocystidia, but in this group they intergrade to a remarkable extent. The point in our plan, which has some significance, is that it is in this group that it appears that we are dealing with a group in which chrysocystidia are originating, and that various stages of development will be encountered, depending on which chemicals or stains one uses to differentiate the physical properties of the cell content.
We have also found that while the morphological types already outlined are in the main distinct, there are many species in which intergradation between types occur. In P. simulans, for instance, the pleurocystidia (as chrysocystidia) measure up to 58 µ long—as long as for many of the Flammuloides-type and are fusoid-pointed. To this one can add other information such as that in a number of the characteristically chrysocystidiate species such as P. prolixa, the amorphous-refractive inclusion becomes red in Melzer's reagent, indicating a chemical difference in the material involved when compared with species in which the chrysocystidial inclusion is merely dingy yellowish to scarcely colored in Melzer's. In P. aurea some of the basidioles, as revived in KOH, have an amorphous content resembling that of true chrysocystidia.
In our estimation one of the most interesting features discovered in the course of the present study is that cystidial shape and content are not necessarily correlated, and that the characterization of "chrysocystidia present" is hopelessly inadequate by itself in describing the cystidia of a Pholiota. A major feature of Pholiota is the diversity in cystidial content—as indicated in our descriptions. It deserves a special study by microchemical tests. It is hopeless to try and limit the term chrysocystidia in this genus to the end-cells of the hyphae of the laticiferous system as these occur in the hymenium. In P. sola we have observed hyphae with the content of oleiferous hyphae which ended in basidia with spores attached and with the basidia having the same distinctive content as the hyphae from which they originated. In short, Pholiota is a most interesting genus from the standpoint of the content of the hyphal cells.
The absence of pleurocystidia is the most difficult feature to use, since one must first search for imbedded cystidia, but there appears to be a group of species in which hymenial cystidia are truly absent. For this group it is actually best to check dried material because it is rather easy to spot the refractive inclusion in the hymenium of a chrysocystidium before one makes out the outline of the cell around it.
Cheilocystidia. By definition these are the hyphal end-cells on the gill edge which do not produce basidiospores. They may be in the form of basidioles, resemble the pleurocystidia in shape, or have their own distinctive morphological characters. They may also have distinctive content in the form of amorphous refractive material or a dull brown homogeneous content. In the subgenus Pholiota in some species the chrysocystidia found as pleurocystidia can also be found in the hymenium covering the gill edge. This is by no means unexpected. The same can be said for the types of pleurocystidia which approach in some measure true chrysocystidia. If fertile basidia occur on the gill edge these types are also to be expected there. In subgenus Flammuloides the cheilocystidia are often smaller than the pleurocystidia but basically the same type.
In general cheilocystidia tend to vary in morphology more than pleurocystidia, but they are typically reasonably constant for a species and in many instances do furnish valuable taxonomic characters. In fact the situation is roughly parallel to that found in Galerina (Smith and Singer 1964). In certain species the cheilocystidia are nine-pin-shaped, in others they are cylindric to filamentous or elongate-clavate, in others they are long- or short-fusoid to fusoid-ventricose, aciculate, vesiculose, spathulate, etc. The length of the neck varies with the species from short and thick to long and narrow and, of course, this is reflected in whether the apex is broadly rounded, obtuse or subacute. In some the neck is not uniform in diameter or evenly tapered but instead is somewhat moniliform, constricted to knobby or more rarely, branched. Encrusted or thick-walled cheilocystidia are rare.
The size varies with the species being small in some (14-20 µ long) and up to 75 µ long in others. Tie range in width for the genus is about like that for Mycena, Galerina and Psathyrella, rarely do they measure over 20 µ wide in the broadest part. Rarely are the cheilocystidia longer than the pleurocystidia. In P. innocuta and in P. simulans the wall may be thickened noticeably over the ventricose portion or the apex. In P. sola they are often septate. In a collection from Alaska they are evidently somewhat gelatinous since in revived sections they usually appear agglutinated to each other. In no instance did we find the dark brown pigment present in a sufficient number of cells to impart color to the gill edge (but see P. fagicola and P. hiemalis with yellow gill edges). However, in species which show darkening of the gill edges from bruising, one can often find numerous colored cells in the damaged zone. This is a feature common throughout the Agaricales including the boletes.
Gill trama. The typical pattern for the genus consists of a central strand of subparallel to slightly interwoven non-gelatinous hyphae with cells varying from 3-6 µ wide, in some species, and to 12-20 µ in others and with some degree of inflation present at maturity. The walls are typically smooth and hyaline to slightly colored but in P. bridgii they are distinctly thickened and dark colored. Since a good share of our studies are from dried material not examined by either of us in the fresh state, we have tried to be conservative in using the degree of cell inflation and width of cell before inflation as taxonomic characters of significance, but it is probable that more detailed studies will reveal more differences on the order of those we have observed: hyphae 3-6 µ diam. as compared to 12-20 µ, and smooth vs. encrusted walls.
Perhaps the most outstanding single feature of the gill trama in Pholiota is the manner in which the hyphae of the subhymenium gelatinize to produce a distinct translucent zone (in KOH or H20 mounts). We tried to correlate this feature with the presence of a gelatinous pileus epicutis and found the following: 1) Species in which both the cuticle of the pileus and the subhymenium are gelatinous. This may be said to be typical for the genus. 2) Those with a dry pileus and dry floccose subhymenium. This is the second largest group. 3) Those in which the cuticle is gelatinous but the subhymenium is not, as in P. atripes, P. brunnea, P. innocua, P. pallida and a few others. 4) Those with a nongelatinous pileus epicutis but with a gelatinous subhymenium as in P. squarrosa, the type of the genus.
Pileus trama. The hyphae composing the trama (context) of the pileus commonly are disposed either radially or interwoven. In the radial type, tangential sections reveal the transverse ends of the hyphae suggesting a pseudoparenchyma. A radial section, however, will reveal the true arrangement and type of element. In the interwoven type, tangential sections merely show the hyphae interlaced. An intermediate type, radial-interwoven, is not infrequent, and is distinguished by radially-disposed hyphae, but these hyphae, instead of being parallel, are interwoven. In some instances, we have described the pileus trama as vesiculose; but whether this condition results from poorly dried material, or represents the true structure is not clear. We have not encountered truly amyloid hyphae in either the pileus cutis or context. However, one reaction we have observed with Melzer's reagent may have some significance. In a number of species, when the pileus context was revived in KOH, the hyphae revived exceptionally well and were seen to have a colloidal appearing content (granular but homogeneous). Sections mounted in Melzer's show these same hyphae to have a cinnabar red to orange yellow content. This is a very striking reaction but one for which as yet the significance is not clear. It is the main difference between Pholiota limonella Peck and P. squarroso-adiposa Lange. However, it is a widespread reaction among the fungi. Smith has observed it in Macowanites (in the astrogastraceous fungi), in Leccinum, in the Boletaceae, and here in Pholiota to name the larger groups. In nearly all of these the very well revived hyphae in KOH with their colloidal-appearing content enabled the Melzer's reaction to be accurately predicted.
In most species examined, the pileus trama is homogeneous and is uniform throughout in structure. In P. stratosa, however, it is duplex; the outer (upper) half being loosely radial-interwoven; the inner (lower) half compactly radial. In P. macrocystis, the outer portion is of large vesiculose elements, and the inner of narrower elements.
Pileus Cuticle. The covering of the pileus in its simplest form is a more or less undifferentiated surface area—not greatly distinct in structure from that of the context. Examples of species in which the cuticle is not sharply differentiated include P. angustifolia, anomala, duroides and scabella. In a slightly more modified dermal layer, surface hyphae are darker and often with thicker walls than those of the tramal area. In some species the surface hyphae are repent, and with a few or no erect to semi-erect hyphae; in such a condition, the pileus is glabrous. In several species, however, hyphae, often darker brown and in clusters, occur in a more or less erect or even reclining position, and are seen on the pileus as scales. In more rare instances, erect specialized cells, clavate or cylindric, are present as pileocystidia. When the hyphae bearing these elements are erect and numerous they form what is known as a trichodermium. This latter type occurs mostly in subgenus Flavidula in varying degrees.
In viscid and glutinous species, a zone of the surface hyphae, when wet, becomes gelatinized. Thus, the cuticle is gelatinous, and in sections in KOH it is translucent, or glassy. The zone may be narrow or broad (50-400 µ), and very distinct under the microscope even under low magnification. In this gelatinous zone, hyphae or hyphal remnants persist for a long time even in mature pilei. Shaffer (1966) has recently discussed the modifications which hyphal walls undergo to produce a viscid or slimy layer (pellicle) and has pointed out how it is possible to have hyphae imbedded in slime (secreted by the cell) without the cell wall becoming involved through disintegration. In Pholiota both types undoubtedly occur but in our studies we were unable to distinguish clearly any cuticle of the pellicle type in which none of the gelatinization came from hyphal walls. In Pholiota the common occurrence is for the cuticle hyphae to have hyphal walls that gelatinize to some degree.
Usually, the gelatinous cutis rests on another zone, usually of brownish hyphae—the hypodermium. The hyphal components of it are often periclinal in arrangement, but in some species are more or less radial, and not infrequently their walls are encrusted. In some species a hypodermium is not differentiated. We regard the hypodermium in Pholiota as the upper zone of the pileus context, not part of the cuticle. This is because of the poorly defined nature of the zone, and too often the only differentiation is the presence of a small amount of pigmentation.
The general type of pileus cutis—whether of repent, dry hyphae, or of gelatinous hyphae—is highly important taxonomically at the subgenus and species levels, and has been used to a great extent in this study.
Pileocystidia. In a comparatively few species, single-celled elements stand more or less erect on the pileus surface. These terminal cells, called pileocystidia, are differentiated, and they may be distinguished morphologically from a mere hyphal tip. We found pileocystidia in tufts in P. canescens and in P. minor. In the latter, they are similar to the cheilocystidia (subfusoid). Likewise, pileocystidia were found rarely in a few other species, but here they were scattered rather than in tufts. We have assigned to pileocystidia only minor taxonomic value since they are not a feature of very many species and those having them are not obviously closely related among themselves. In subgenus Flavidula they form the terminal cell of the trichodermial hypha and are treated as part of the trichodermium.
The stipe cutis, with few exceptions, is dry; in P. adiposa, however, the hyphae of the scales on the stipe are gelatinous. This is a diagnostic character for P. adiposa and a few other species. In a large number of species in subg. Flammuloides the hyphae at the stipe apex darken strongly in KOH. This is a feature of some significance, especially in the study of dried specimens.
Caulocystidia. In all Pholiota material examined in this work, longitudinal sections of the stipe apex (between the pileus and the annular zone) have been prepared and have been examined for caulocystidia. In many species caulocystidia were absent; in many others they were present and readily found. In instances where present, their morphology, is one of two types: 1) those which were similar to the cheilocystidia (or even the pleurocystidia, if present); and 2) those which differed in shape from the lamellar cystidia. In general, they may be scattered along the surface, or, in some species, may occur in distinct clusters or rosettes.
The taxonomic value of caulocystidia is, in our view, somewhat uncertain. In some collections of a species, they were found; in other collections of the same species they appeared to be absent. This situation was encountered sufficiently in these studies to cause avoidance of any considerable use of these structures in the separation of species or larger entities. Further study of their occurrence is necessary to a clear understanding of their significance in Pholiota systematics, but studies should be based on fresh material. Large thin-walled vesiculose cells in particular are often difficult to revive.
Clamp connections. For practical purposes, clamp connections were found in all species of Pholiota studied (except for P. fulvosquamosa and P. cinchonensis). In rare instances, we assume that they escaped detection, either because they were very small and inconspicuous, or they were indeed very rare in their occurrence. We are not yet ready to assume that when not found in the course of ordinary examination they are not present to some extent somewhere in the basidiocarp. Because of their (almost?) universal presence in Pholiota, they offer no help in the separation of taxa, a situation in contrast to that in the genus Crepidotus.
KOH was used as a standard mounting medium and the usual darkening of hyphal walls from ochraceous to rusty brown was noted as occurring but has not been given particular emphasis in infrageneric classification simply because it did not seem practical. No red or green reactions as one frequently finds in other genera—Panus, Cortinarius, etc. were noted. KOH on the fresh basidiocarp usually gave some degree of browning reaction, but more studies are needed here as our data are necessarily incomplete, though the KOH reactions are apt to be at least somewhat similar on both fresh and dried material. KOH often dissolves the yellow to brown pigment to some extent. This is readily observed in the mounting medium.
FeS04 has been tested to some extent, mostly in recent years, and the typical reaction is olive to bright green. From preliminary studies we suspect most species of reacting, but the time required for the color change may vary considerably. Hence some reports of negative reactions may be unreliable. The situation will probably turn out about like it has for Inocybe (Stuntz per. com.) and our observations verify his, namely that here also almost all species react, but some more slowly than others. We have obtained green reactions with P. macrocystis and P. flavopallida, malachite green in P. agglutinata, instantly olive in P. lurida, P. milleri and P. stratosa and in P. molesta no change at all.
The reactions with Melzer's reagent are interesting and of considerable help taxonomically in some areas. Subgenus Flammula, as indicated elsewhere, is defined on the combination of dextrinoid spores and lack of pleurocystidia. We regard it as unusual that the spores of so many species of Pholiota are paler in Melzer's reagent than in KOH. In one species, P. brunneidisca, a few of the spores showed a dark purple-brown content—a feature unique in the family Strophariaceae as far as we are aware, and for which we have no explanation. The pileus context gives a bright orange-red reaction in Melzer's reagent as noted for P. limonella. This character is found in Macowanites, Pholiota and Leccinum—to name some obviously unrelated groups. It can usually be predicted by the colloidal appearance of the cell content in KOH as previously pointed out. As yet we need data on fresh material of these fungi to ascertain the difference in the reaction between fresh and revived hyphae. Our studies on this feature are from dried material revived directly in Melzer's reagent.
A critical study of the cystidial content of all Pholiota species is now in order to explore the value of the content as a taxonomic character, and to evaluate the category of chrysocystidia in relation to differences in chemical content of these organs.