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

24

THE BOLETES OF MICHIGAN

not a question of whether a slight difference in the arrangement of
hyphae in the hymenophoral trama can be demonstrated, for we have
done this, but rather what does the slight difference mean?
We regard the group starting with section Piperati to be the trunk,
so to speak, of the evolutionary "tree" of the boletes.
As to the overall evolution of the boletes, we visualize Gyroporus
with its very pale spores as perhaps being relatively primitive, but along
with it we consider Suillus as being close to the point of origin. At least
3 lines can be followed in Suillus. One, as pointed out, leads to
Gomphidius, another to section Piperati of Boletus, which presumably
originated from the more unspecialized species of Suillus, a third to the
highly evolved species of Suillus, such as S. luteus, in which one finds
both a distinctly glandular dotted stipe and a characteristic annulus.
From section Piperati it is easy to visualize a connection to the B.
pallidus and B. badius types and these clearly lead into the more xerocomoid fungi of the section Subtomentosi. Throughout this progression,
as in all major lines, we have "Anhang" species such as B. parasiticus
which have made unusual adjustments-in the present case an ability
(dependency) to parasitize species of Scleroderma (a gastromycete). At
present Phylloporus is placed in Paxillaceae, though it does have some
features of the Subtomentosi.
Gastroboletus, the gastromycete with Boletus-type gleba, is regarded as an artificial group in the sense that these species have evolved
independently from various lines in the family Boletaceae and are more
closely related to their parental types than to each other. The question
of the origin of the boletes is an open one. Two possibilities suggest
themselves: first, an origin from Suillus-like ancestors in the Gastromycetes, Truncocolumella for instance; and second, origin from
Gomphus-like ancestors. As yet neither possibility has been explored
sufficiently to give an unequivocal answer.
Lastly, one must always keep in mind that all taxonomy is tentative and is continuously being modified by more information on individual groups. As yet we lack biological studies on most of these
fungi, and when these are made, they will certainly modify taxonomic
concepts arrived at from a study of material collected in nature. This is
not an idle generalization. The boletes as a group are so closely related
that the problem of gene exchange across taxonomic categories, when
we have reliable information, is bound to modify existing concepts. For
instance, all of the boletes in section Subtomentosi are in a sense so
closely related that one is inclined to interpret the various combinations