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

The North American Species of Pholiota

In the Lake States Pholiota squarrosoides is one of the major causes
of decay in logs of Acer saccharum and Tilia glabra. In fact the decaying
trunks of the latter are reduced in very short time. Smith followed the
course of decay in one tree near Ann Arbor. The log was relatively
sound when discovered with a few basidiocarps of P. squarrosides on it.
Four years later there was almost nothing left of it. In the interval, during two seasons, large masses of basidiocarps were observed. P. albocrenulata causes a heart rot of maple trees, at least the basidiocarps occur
in a pattern indicating this, but we have no data of our own to indicate
the extent of damage produced or the rate of decay. The fungus can
attack trees down to 6" DBH. In fact, P. albocrenulata is to be regarded
as one of the characteristic species of the beech-maple association, but was
found on ponderosa pine in New Mexico by Barrows and Isaacs.
Cottonwood and Lombardy poplar are commonly attacked by Pholiota destruens. This fungus appears to form a primary decay as fruiting
bodies often occur on the cut surface of the stump or log-ends. This species
has been studied in some detail in culture.
Anyone collecting in irrigated country where Lombardy poplars
were planted along the ditches many years ago has probably seen this
species. These trees are now being cut down because of die-back and
over-maturity. One will find this species in quantity on the stumps or logs
during cool wet weather in November. On one trip through the John
Day country of Oregon during November, we observed basidiocarps of
this species on almost every log or stump of cottonwood or Lombardy
poplar in a fifty mile stretch.
In summary, we can say from our own observations that Pholiota
is a genus in which physiological specialization has progressed along the
lines of using various components of wood for its nutriment, and no
mycorrhizal forms clearly belonging here are known. The opposite is
true for Hebeloma in which it is very likely true that all or nearly all the
species are mycorrhiza formers. As we have treated Pholiota here we regard it as the major genus of wood-rotting agarics having colored spores.