The boletes of Michigan, by Alexander H. Smith and Harry D. Thiers.

INTRODUCTION

23

much more homogeneous than in its original sense. Of the groups recognized in it here we would single out for comment first of all subsection
Luridi of section Boletus. It is based primarily on the color of the
pores-orange to red to brown-but the core of the subsection is composed of species with very narrow (3-7 g) hyphae composing the cuticle
of the pileus. In addition to this core of related species we find, in
groups separated by other characters, species with colored pores, as in
Leccinum, which are not closely related to the Luridi. In other words,
for the most part Luridi is a typical natural group even though the
index character for it may seem superficial to some. It is true that the
character of colored pores simply has its basis in pigment dissolved in
the cell sap of the cheilocystidia. Such occurrence of pigment in special
cells is well known throughout the fleshy fungi-it is almost routine.
Mycena and Lactarius are relatively unrelated genera of gilled fungi
which have species featuring the character.
Subsections Calopodes and Boleti of Boletus represent the core of
section Boletus. We regard them as forming an end line in the evolution
of those species with a Boletus-subtype arrangement of the hyphae of
the hymenophore. We still need a truly critical account of the edulis
group for North America-and for the world for that matter. It is in this
group that new characters, such as iodine reactions on spores and context tissue, will aid in clarifying taxa. B. calopus is a good example, for
in it the transverse septa of the hymenophoral hyphae have blue walls as
mounted in Melzer's (see Watling & Miller, 1968). But as is evident from
the tone of this whole discussion, these new characters need to be
studied in all groups in the family to ascertain if a pattern of evolution
can be established showing how they reached their present degree of
development.
One genus left out of our system, and which each of us at one
time or another has accepted, is Xerocomus. We have divided the species
of this group on other features than the velvety to subtomentose pileus,
wide tubes, and the arrangement of the hyphae of the hymenophoral
trama-the Phylloporus subtype-by which the genus is currently defined. One reason for abandoning the genus is that other workers, Singer
included, who have accepted it have not in their own work showed that
they had a clear concept of what the genus should be. We have found it
an impractical grouping as far as identification is concerned, and the
relationships in section Subtomentosi do not follow well the guidelines
laid down for recognizing the genus. In its makeup it seems comparable
to subsection Luridi-a core of related species and others not related but
with some of the stated diagnostic characters of the group. To us it is