Of all the genuses, Psathyrella might have had the most convoluted wrangling about what species belong in it, although there are several rival candidates among the dark-spored mushrooms. Kauffman, probably the most respected American mycologist of his day, said in 1918 that as an Agaricus subgenus, Psathyrella Fries (1838) refers to a tiny genus having the type species Ps. disseminata Fr. It was characterized by being Coprinus-like, but non-deliquescing, having black spores, a membranous, plicate to sulcate pileus, slender stem, vanishing veil, and gills that do not become variegate-dotted (to distinguish it from Panaeolus and some species of Coprinus). Kauffman says that Peck described 12 species, but that he had personally only seen one other, cretata (Lasch Fr.), which I have not seen mentioned more recently either in the U.S. or Europe, so a different name is apparently used now. This concept of Psathyrella lasted in the popular U.S. literature through Graham (1944), but has now been replaced by a completely different one. Everybody calls the new genus Psathyrella (Fr. Quél.). Singer says (1986) that Quélet decided in Champ. Jura Vosg. (1872-3) that Fries had gotten the type species of Psathyrella Fr. wrong because this species "did not fit the synopsis" that Fries published (although it appears to me to fit the one Kauffman says Fries published). He therefore rejected Fries' type species and replaced it with Psathyrella gracilis (Fr. Quél.). That seems reasonable enough; gracilis fits what Kauffman lists as the synopsis for Psathyrella just fine (as does disseminata). I have not figured out what Kauffman called gracilis yet, but it is common enough that he must have had a name for it.
By a logical process I do not pretend to understand, other authors expanded Psathyrella (Fr. Quél.) into a huge genus, incorporating part of Hypholoma (Fr. Quél.) and all of Psathyra (Fr. Quél.). The original Psathyrella type species disseminata, after spending a while in Pseudocoprinus (Kummer), has been reabsorbed into Coprinus in most modern books. This appears to demonstrate again that current mycologists don't really care about macroscopic features, since the principal reason Fries separated Ps. disseminata in the first place was that it does not deliquesce. Why they would completely change the definition of a Friesian genus (and pretend that the Rules of Nomenclature somehow justify it) escapes me. If one can both change the type species and eliminate the original one from a genus, the new genus can have no overlap with the old one, as occurred for Psathyrella. How could people want it to have the same name, and why would they devise Rules that would make this happen?
Modern Psathyrella has spores that vary from blackish through brown, purplish brown, and pinkish gray (so spore color doesn't help much to tell if a species is a Psathyrella), but apparently browns in the yellow-to-orange range are excluded. Other characteristics are a veil that varies from absent to copious and persistent (so veil characteristics don't help either), a cap surface that varies from smooth to grooved all the way to hairy (also of no use), a stem that is "usually" fragile and whitish, and complex combinations of microscopic features. This genus concept obviously has nothing whatsoever to do with what Quélet was talking about in 1872-3 (he recognized both Hypholoma and Psathyra), so calling the genus Quélet's modification of Fries's name without giving a reference is only confusing. It solved some other nomenclatural problems: Hypholoma was hopelessly diverse, containing both the species people want to call Naematoloma now, and ones that are Psathyrella. I have not seen what was wrong with the name Psathyra. Quélet used Drosophila for a united genus in 1886, but it was later declared to be an invalid name, although no one I have read has bothered to say why. I hesitate to think that the fact that it is used for a genus of fruit flies has anything to do with it.
Smith published a monograph financed by the National Science Foundation on North American Psathyrella in 1972, describing over 400 species, divided into ten subgenera, although a few have only one species each. Most of the large number of new species reported in it do not appear to have been used by anyone else since. The majority of them were found either near Ann Arbor, Michigan (Smith's home), or Lodgepole, Idaho (where he spent summers with his wife, who both was from there and was working on a paleontology degree in the area). Smith comments that a good year for Psathyrella occurs only once about every 10--15 years, and that in a good year not only are there an order of magnitude more individuals than in a bad year, there are also an order of magnitude more species (hmmm. . .). His monograph finishes with a large appendix containing many new species, and the comment that a third good year had occurred after the main part was finished. I have heard a professional mycologist state that, in his opinion, Smith had a tendency to describe aberrant individuals as if they were species. Although the greater than 400 species number is sometimes repeated, the only general book I have seen that describes even as many as 9% of this number is Smith, Smith and Weber (1979), who cover 35. Singer (1986), who likes a lot of species as well as most, only recognizes 74 Psathyrella species worldwide, acknowledging that many more have been named, and mentioning that species concept in Psathyrella is "not settled" (which appears to most often mean "people still refuse to use my concept"). Smith's monograph has made it improbable for any amateur to conclusively name almost any Psathyrella, because Smith's species are based on extremely detailed microscopic features that I certainly don't know how to demonstrate.
Psathyrellas are the quintescence of "little brown mushrooms" to most people, and I don't think any are considered good to eat. David Arora (1986) believes that "They constitute an immense, monotonous, metagrobolizing multitude of dull, whitish, buff, graying, or brownish mushrooms. . . ." (he does have a tendency to get caught up in his own rhetoric, doesn't he?). Although Psathyrellas are quite common, most mushroom books ignore them as completely as possible. Only five are illustrated in Bessette, Bessette, and Fischer, and twelve in Phillips (all rather ugly-looking fellows). I agree that many Psathyrellas are quite ignorable, especially in age, but think that when they are young enough, some have a quite striking appearance.
Here are photographs of three striking Psathyrellas.
The cap of this species is a rich reddish brown and the beautiful
corrugations arehighlighted with white, possibly remains of the white veil. It
was found in Baxters' Hollow (Sauk County on an October 1st, and I am calling
it Ps. deliniata (with relatively little hope of it actually being this
species).
This species has deeper brown cap color and a contrasting,
abundant bright white veil that clings to the margin in gobs. The stem is rather
thick for a Pathyrella, and also a bright white. It is also from Baxters'
Hollow, on a September 5th.
I call this Psathyrella the "spring dot-cap" because I still
don't know exactly what it is. We often find it in May, instead of the Morels
we're hunting. It grows on well-rotted wood, has rather persistent hair-like remnants
of a veil on both cap and stem, and is slightly hygrophanous. The picture was
taken at Ferry's Bluff, Sauk County, on a May 13th, and I don't believe that I
have seen this species after the first of June.
Psathyrella species (whose names I naturally am not completely sure of) provide excellent examples of some technical terms used in books describing mushrooms. One of the irritating things to a beginner is the frequency with which people make up special jargon to conveniently describe things about plants. The jargon words usually don't mean anything in the absence of knowing exactly what they were made up to designate without wasting a lot of time explaining in real English words. All areas of science do this; it is necessary to prevent wasted effort. Nevertheless, using jargon sure makes it harder to "join the club" and figure out what the descriptions mean.
Covered with flakey looking scales,
usually arising from tearing of a fragile veil as growth occurs. This Psathyrella,
found on an October 27th at La Riviera City Park, Prairie du Chien (Crawford County),
has both floccose cap and stem (usually called the pileus and stipe by mycologists),
and is probably in Smith's Subgenus Pannucia, Section Pannucia,
which has many floccose species, although it is larger (5 cm) and shaggier than
illustrations I have seen of P. pannucia itself. 
Having sufficiently loosely packed
hyphae in the cap so that water is soaked up like a blotter, producing very large
differences in color between "soaked" and dry conditions. The figure to the right
shows Psathyrella hydrophylla, taken on a May 30th in the UW Arboreteum
in Madison (Dane County), and you can see completely dried as well as completely
hydrated caps close to each other. This is one of the commonest species, illustrated
in most books. You clearly must be very careful about matching colors to ones
in photographs for hygrophanous mushrooms, as their appearance changes greatly
with time, even within a couple of hours after picking. This makes photographs
of strongly hygrophanous species that were carried to a laboratory to photograph,
as for example in Phillips' books, look rather different than they did in the
woods. Most Psathyrella species are at least slightly hygrophanous, although
the degree varies a lot. 
Fragile and disappearing. The
fragile, wispy grayish veil still remaining on the turned over mushroom cap is
quite evanescent. No trace of such a veil was seen on any of the other caps in
this cluster. It is common not to be able to find traces of evanescent veils and
rings on any of several mushrooms, making you wonder whether there ever was one.
Nevertheless, whether there is a veil is frequently a branch point in keys (and
one of the reasons they are hard to use; if it appears high in the key, you often
have to follow both pathways all the way to their end, or get the wrong answer).
The cap is also hygrophanous, and unusually, dries in streaky patches starting
between the margin and the center. I have no idea what this Psathyrella
is. The picture was taken at Whitefish Dunes State Park in Door County, on a September
11th. 
Sometimes `Englished' as "lined",
this means that although the surface of the cap is smooth, it is semi transparent
when hydrated, so darker regions are seen above the gills. When dehydrated, the
cap usually becomes opaque, and the "lines" can no longer be seen (so virgate
mushrooms also change greatly with age). I am not absolutely certain that the
mushroom shown on the right is a Psathyrella. The stems are rather thin
and fragile, but not white. It has a Mycenoid aspect, that is, it looks like some
Mycena species. The photograph was taken on an October 1st at Rowan Creek,
near Poynette. 
This species is strongly hygrophanous (which would not be
obvious if I had not set one cap that was dried out near the others), clearly
has an evanescent white veil covering the cap (most obvious as the tiny flecks
on the margin of the smallest cap), and rather unusually, also has a persistant
membranous ring, formed from a partial veil between the margin of the cap and
the stem. All of this has unfortunately not allowed me to tell what species of
Psathyrella it actually is. Taken on a September 11th at at Whitefish Dunes
S.P. in Door Count
This Psathyrella species is probably in Subgenus Pannucia,
has persistant white veil remants that hang on the pileus margin in triangular
tufts as well as very fine "hair like" remants on the rest of the cap, and is
faintly virgate. I have seen it several times, both in the spring and fall, but
this picture is from Baxters' Hollow on a June 30th.
This Psathyrella has a cap that is virgate all the
way to its broad umbo and the surface is tacky when wet, as it was in this picture.
I am trying to convince myself that this is Ps. verna. The photo was taken
on a May 17th, at Wyalusing S.P. in Grant County.
This Psathyrella borders on Aurora's "monotonous multitude",
but is seen to have a generous amount of white veil when it is young. The veil
is evanescent and disappears from most specimens the the time the cap is fully
expanded. The fragile, whitish stipe is typical of the genus. The picture was
taken on a September 20th at the Madison School Forest in Verona, Dane County.
This mushroom has a mycenoid aspect but dark spores. Its
pileus (cap) is campanulate (bell shaped) and strongly virgate (transparent when
hydrated) all the way to the umbo (center of the cap when it is raised) revealing
rather close (closely spaced) lamellae (gills), and is strongly hygrophanous ,
drying from the umbo toward the margin (edge of the cap). The cuticle (skin) of
the pileus has very large, swollen cells, which occurs in some species of Psathyrella,
but I am not even certain of the genus of this mushroom. It was photographed on
an October 26th in Wyalusing S.P., Grant County.
