The North American species of Pholiota, by Alexander H. Smith and L. R. Hesler.

Smith * Hesler

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Hispidoderma-a tangled mass of hyphal end-cells cystidioid in shape.
As the shortening process continues the cystidia become shorter and more
compactly arranged until a hymenium-like layer results. In Pluteus it is
certainly evident that the hymeniform type of cuticle could have originatedl in this manner with fewer changes in the genome of the group
than by any other means.
The same explanation of this formation of the trichodermium of
Phacomarasmius is equally as plausible. The name Pholiota means scale
and this is the keynote to a good share of the genus. Here we find what
we have termed the "collapsed" trichodermium meaning that the layer
is sparse enough when the pileus is mature so that the hyphal elements
do become more or less decumbent as the pileus expands. Since we have
filamentous, intermediate (collapsed trichodermium) and trichodermial
types as well as the granulose type in Pholiota, it appears more logical
to us to assume that the more complex type evolved from the undifferentiated type.
On this basis we do not admit that the cuticle types as used by Singer
have any value in delimiting genera in the present case. The color of the
veil in P. proximans is much like that of P. curvipes, so we also exclude
veil color as having any generic significance. In fact, it seems clear to us
that the major aspects of evolution in Pholiota have been concerned with
cuticle types.
In view of the strong likelihood that the trichodermial type of
cuticle originated in the manner just discussed, we consider Phaeomarasmius as a genus to be distinguished by its more or less eccentric stipe
in addition to the cuticle type (trichodermium), and large spores as proposed by Singer. In this way, the genus is found to occupy an end position in the Flavidula branch of Pholiota. That so many intermediate
species are still in our flora, can hardly indicate that more genera should
be recognized. We regard the Flavidula line to have bifurcated with
species having a Cystoderma-type cuticle as one branch, and those leading
to the P. erinacea type forming the other.
Thus Pholiota aurea appears to us to be more in the "orbit" of
Pholiota than in Cystoderma. Because of its size it is very distinct from
the other species, but the same size range (or nearly so) is found in
Cystoderma. The thin-walled at times slightly ornamented spores are the
best reason for excluding P. aurea from Pholiota. This point should be
studied by EM photographs.
One uniting feature of the whole group (Flavidula) as we have
outlined it is that the hyphal walls become a darker brown or change
to brown upon the application of KOH.
We do not put any generic emphasis on the presence or absence of
cheilocystidia as we feel that this is a more minor character best used at
the species or section level.
A second feature which rather well unifies this whole subgenus is