The North American species of Psathyrella.

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MEMOIRS OF THE NEW YORK BOTANICAL GARDEN

[VOL. 24

trivial. There is also the practical consideration that if each slightly odd agaric
is made the type of a genus, agaric taxonomy will certainly fall into disrepute.
Macrometrula Donk & Singer can be recognized by the large membranous
volva, again a single character. Otherwise it appears to be a Psathyrella.
Since the volva is at such an advanced stage of evolution as compared to any
Psathyrella known to me, and since I have not seen fresh material of Macrometrula, the disposition made by the original authors is accepted.
In summary it can be stated that the genera surrounding Psathyrella show
the same pattern as the genera surrounding Cortinarius-namely odd segments
of evolution in the form of satellite genera.
EVOLUTION WITHIN PSATHYRELLA
If it is assumed that the genus originated from primitive types in the
Bolbitiaceae, we can at least introduce the present topic in a logical manner,
for, as previously mentioned, in the Bolbitiaceae we find nearly all the anatomical
features which also characterize Psathyrella. Both groups are saprophytic, both
have a cellular pilear cuticle, both have similar spore anatomy, both feature
rather similar cystidia, and enough intergradation in the color of the spore
deposit exists to cause some confusion between them. Brachybasidioles have
evolved in both groups. All this points to the fact that evolution did not bring
about much change in creating the group now known under the name Psathyrella.
Major points of difference appear to be in the development of the outer veil in
part of Psathyrella, and the pigmentation of the pileus is also different, especially
the reaction of the pigments to KOH. The major lines of evolution in Psathyrella
are as follows:
Lacrymaria (subgenus). This is one of the most highly evolved groups in
the genus and to me represents an endpoint in evolution. The arguments for
recognizing this group as a genus are as good as those for Macrometrula. It is
retained here because it is likely that it can be connected up to the following
subgenus.
Psathyroides. This group could have originated from the same ancestral type
as Lacrymaria, but species of Psathyroides show a more smoothly intergrading
series of characters leading into the typical Psathyrellae. The evolution in these
two groups seems to be away from the Coprinus type basidiocarp.
Pseudostropharia in reality consists of two lines, one with apiculate nontruncate spores which is the type section, but the heavy veil is the key character.
Pleurocystidia seem to connect the group to cystidiate species of subgenus
Pannucia. The second section, the acystidiate species clearly connects up to
the Candolleanae, in fact, in North America, we have annulate forms of the
latter (see P. incerta and P. candolleana). This group also connects to Pannucia,
especially the acystidiate species.
Homophron contains a number of stirpes but as a subgenus is artificial. It is
recognized more for convenience in ready identification of collections. The
various stirpes connect to subgenera Pannucia and Psathyrella.
Pannucia and Psathyrella as subgenera represent the core of the genus and
the problem here is not the recognition of related lines since relationship could
be postulated in almost any direction, but is rather one of finding groupings that
will be practical in the identification of the various species. It is in these two
subgenera that one can trace steps toward the evolution of the Coprinus-type
basidiocarp.