Many species of Leccinum occur in ecosystems that seem maliciously designed to frustrate precise documentation of mycorrhizal hosts. The northern counties of Michigan's Lower Peninsula represent one such area, and Smith's concept of Leccinum speciation is based in large part on extensive collecting in this region. But separating aspen, birch, and various conifers as potential hosts in Emmet and Cheboygan counties can be a monumental task. I have assured myself that I collected the birch-associated Leccinum holopus under aspen and hemlock in Emmet County, only to return the next year and notice the tiny birch sapling hidden in bushes a few feet from the collection location. Similar host determination problems occur in transitional "aspen zones" in montane ecosystems, though the list of tree species is often somewhat shorter.

Ideally we would have, for example, 100 collections of Leccinum rugosiceps with identification supported by molecular and morphological data, and a long list of potential mycorrhizal associates for each collection--which a computer could sift through for common denominators, arriving at a list of a few well supported hosts. I use Leccinum rugosiceps as my example because, while present data suggests fairly convincingly that the species is mycorrhizal with Quercus and that the rigorous ecological documentation I am proposing is not needed, there might easily be a precise host (Quercus rubra? "red oaks" in general?) that has not yet been determined.

In the present study I have consulted Leccinum collections in the extensive online databases of five herbaria (TENN, OSU, MICH, NY, and BPI) for ecological data, but this strategy should be seen as a desperate substitute for working with reliably recorded, carefully documented ecological data--and conclusions drawn from existing herbarium data on ecology should be read as extremely tentative. Even the best and most prominent collectors, many of whose Leccinum collections are in these online databases, did not hold ecology to be as important as it has turned out to be; as a consequence the data regarding potential mycorrhizal associates is minimal and unreliable.

Most macromorphological characters in Leccinum should be noted in the field--especially the color of the scabers and the staining reactions of the sliced context. Ideal collections include specimens in all stages of development. In situ photographs from all angles, using diffused flash (see Kuo 2004 for basic techniques with digital cameras) should be accompanied by photographs taken in the laboratory or at home.

Pileus. Color of the pileus, while not negligible, may not be as informative as traditional treatments have supposed. In the European context, den Bakker & Noordeloos (2005) argue that molecular results demonstrate many species are capable of displaying a range of light to dark colors. Texture of the pileus surface also demonstrates a certain amount of variability, though some species are consistently fibrillose-squamulose, glabrous, etc. The margin of the pileus usually projects at least a millimeter or so beyond the tubes when the mushroom is young, but by maturity species in subsection Leccinum display substantial overhanging marginal flaps of tissue. One North American taxon, Leccinum potteri, features veil remnants on the young pileus surface.

Hymenium. The color of the tubes and pore surface in both young and mature specimens should be recorded, together with bruising and staining reactions. Standard measurements (depth of the tubes, number of pores per mm) should be taken from mature specimens.

Stipe. Since proportions of the stipe may have some relevance in the North American context (for example, in separating Leccinum crocipodium), diameter measurements should be taken from young and mature specimens at the apex, the widest point, and the base (the point of insertion into the substrate). The "ground color" beneath the ornamentation should be recorded, together with textural surface details (many species develop soft ridges or even quasi-reticulation, aside from the scabers). Some species demonstrate bluish or olive stains on the stipe surface, usually in the basal region. The size ("fine" or "coarse") and density of the scabers should be assessed for the upper stem, the midportion, and the basal area. Scaber color across the developmental stages has proved to be very important in the European context, and the present treatment holds this character (together with its microscopic corollary, the staining reaction of caulocystidia in KOH) as a primary hypothesis for potential morphological separation of North American material. Since the contemporary concept of Leccinum has freed us from the debate over whether darkening of the scabers to dark brown or black is indicative of the genus, we may now be able to describe scaber color more objectively; with no disrespect intended, I suggest that some of the Smith & Thiers descriptions of scaber color (especially those supported by one or a few basidiocarps) may have been unconsciously loaded with the need to justify their position in their argument with Singer, resulting in darker mature scaber colors (or assumed darker colors). The color of the scabers in both buttons and mature specimens should be recorded--but "[c]are should be taken in using this character when the fruit-bodies are found in high vegetation" (den Bakker & Noordeloos 2005) since grass, tall sphagnum, or substrate material can keep light from the scabers and affect whether they darken or not.

Context. The color of the context in Leccinum ranges from white to pale yellow. Staining of the sliced context, while not irrelevant, has probably been given more taxonomic priority in the North American context than variation (and consistency in methodology) should allow. In particular, the presence of a pinkish staining stage before the stained surface resolves to grayish or black has likely been overemphasized. In the European context, staining and the eagerness of the staining reaction have been found to be occasionally informative, but generally so only in limited taxonomic areas (for example the consistently weak staining of Leccinum vulpinum). Some species usually display bluing flesh in the stipe base or in the pileus, but the bluing may not be consistent enough to justify taxonomic priority. Staining reactions should be documented at the time of collection when the mushrooms are fresh.

Spore Print. While spore print color has been used as a predictive character frequently in traditional treatments of Leccinum, it has also been the source of considerable confusion resulting from the difference between a "wet" and a "dry" print--and the character has occasionally been "fudged," as in Smith, Thiers & Watling (1966), where spore print color plays a major role in the key but taxa with undocumented print colors are found subsequent to choices emphasizing the character. In the European context den Bakker & Noordeloos (2005) do not even bother to record or discuss spore print color. While I doubt that the character has any predictive value in the North American context, either, it may be worth continuing to record the print color and preserving prints along with exsiccata--at least until substantial research documents the potential futility of the effort.

Odor and Taste. To my knowledge odor and taste, which are almost universally "not distinctive" in the genus, have not been found to have substantial variation or predictive value within Leccinum.

Exsiccata. Examination of the macromorphology of exsiccata falls into two categories: attempting to recapture details the specimen manifested in the fresh state, and assessing macromorphological features that result from the drying process. As for the first category, it is obviously preferable to examine a fresh specimen or photographs of the specimen in the fresh state, and macromorphological observations based solely on examination of exsiccata should be seen as tentative. In the second category, features resulting from the drying process that may have some predictive value in limited taxonomic areas include the color of the pileus, hymenium, scabers, and context as dried--but variation in drying methods and the age of herbarium specimens may influence these features.

Micromorphological characters that appear to have predictive value in some taxonomic areas of Leccinum (when placed in ecological and molecular context) are derived from observation of the anatomy of the pileipellis, the hymenium, the stipitipellis, and the basidiospores. For the latter, a spore print is the ideal source of material and a water mount will suffice. A radial section of the pileus surface containing about 1 mm of the pileus context for visual orientation should be mounted in unstained, 2-5% KOH or in water. The hymenium should be sectioned perpendicular to the tubes and mounted in unstained KOH. The stipitipellis should be sectioned by slicing a paper-thin section in the mid-portion of the stipe, parallel to the stipe surface, including at least one scaber (in specimens where scabers are clearly defined), and mounted in unstained KOH. If a spore print is unavailable, the hymenium and stipitipellis sections will provide spores for observation if the material was mature. When examining exsiccata, I have found these sections to be more easily accomplished without preliminary rehydration in alcohol and water--and I have compared results from rehydrated sections and straight-to-KOH sections without finding any differences.

Pileipellis. In the European context, den Bakker & Noordeloos (2005) found "two basic types" of pileipellis in Leccinum: a "trichoderm with erect chains of elements" and a "complex type of intricate trichoderm, often with a cutis-like suprapellis." For the sake of convenience the authors call these types "trichoderm" and "cutis"; I have also used this terminology. Additionally I have used the admittedly imprecise term "epithelium" to refer to a trichoderm-like pileipellis in which terminal elements are substantially swollen. Precise documentation of the anatomy of the terminal elements of a trichoderm-like pileipellis may have some value in the North American context; Leccinum rugosiceps, for example, appears to manifest swollen penultimate and antepenultimate elements with consistency. However, the presence or absence of "cylindrocysts" (see Lannoy & Estades 1995), together with the formation of pigment globules in a Melzer's reagent mount (see Smith & Thiers 1966), represent characters that appear not to occur with reliable consistency, and can now safely go unrecorded.

Hymenial Cystidia. Den Bakker & Noordeloos (2005) found "no diagnostic value" in the morphology of hymenial cystidia among European Leccinum species; they found shapes and sizes to vary without consistent correlation to genetic species. However, data on hymenial cystidia is inconsistently recorded in the den Bakker & Noordeloos treatment, and the color of the cystidia in a KOH mount (particularly the cheilocystidia on the pore surface, which tend to display more pigmentation) may turn out to have limited predictive value (perhaps paralleling the KOH reaction of the caulocystidia) and should not yet, in my opinion, be discarded as a potentially valuable character.

Basidiospores. While careful documentation of basidiospore morphology should be continued in North American Leccinum studies, we should probably not expect the data to reveal much for potential species diagnosis. Spores in Leccinum are often quite variable in size, and exceptional "monster" spores are not infrequently encountered. Additionally, the current data on spore morphology in North American Leccinum cannot be relied upon, due to inconsistencies in methods: immature spores have undoubtedly been included; little or no effort has been made to account for potential differences in dimensions of spores produced in the tubes or on the stipe; mounting media have been inconsistent and poorly documented. In the European context den Bakker & Noordeloos (2005) found spore shape (not length, in and of itself) to have some potential value as a character; researchers who want to generate basidiospore morphology data that can successfully be compared to the data of den Bakker & Noordeloos should follow the same methods:

"Spores were mounted in demineralised water and observed under oil-immersion. Only spores from the (pileal) hymenium were used and an attempt was made to measure only mature spores. Spores were considered mature when a clearly developed, slightly (brownish) coloured spore wall was present and guttules could be observed within the spore. Sometimes extremely elongate spores (Q > 4) were present in the hymenium of older fruit-bodies. These are considered anomalies, probably associated with unnatural aging of the fruit-bodies. These were not included in the measurements. Circa 30 spores per collection were measured."

Caulocystidia. Caulocystidia in Leccinum vary substantially, and in most species a wide variety of cystidia shapes can be demonstrated. However, in some species one or a few types of caulocystidia represent the overwhelming majority, and are easily demonstrated without a painstaking search. Additionally, the color of caulocystidia as mounted in KOH appears to have some consistency and, consequently, diagnostic value in limited taxonomic areas. Relatively little attention has been paid to caulocystidia by North American (or other) researchers--but since caulocystidia represent, in part, a microscopic corollary to the scabers, which den Bakker & Noordeloos (2005) have found to be substantially more worthy of attention than was previously suspected, it is worth maintaining the hypothesis that careful documentation of caulocystidia may help support identification--a hypothesis used by den Bakker & Noordeloos with success in the European context.