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

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North American Species of Crepidotus

the practical use of this character in identification work. It is essential, of
course, to get some indication of the color in order to identify the genus.
Spore size is a routine feature in Crepidotus, as in other agarics, and our
observations have shed no new light on the pattern of variation within species or its use in delimiting species. The range in spore size for the genus,
about 4-10 It in length, is one of the narrowest for any agaric genus. Because
the ornamentation of Crepidotus spores is not prominent, as it is in many species of Lactarius, our measurements always include the ornamentation, if any
is present. Spore shape, in our estimation, is a more important feature than
spore size. It is a very reliable character at the species level and serves well
as an aid in circumscribing infrageneric taxa. One must be sure to view the
spores in profile view as seen on the sterigmata as well as in the front or back
views. Crepidotus spores fall in the category of "thick walled." At least the
wall is fairly rigid, but in most species it is scarcely thick enough to measure.
Basidia. From species to species, basidia vary some in size, but with the
evidence at hand we feel that the differences are of little value taxonomically. The variation in a single cap is often very great. It is important to note
the size in descriptions, however, since the information may be useful to
some investigators, such as cytologists engaged in studies of the basidium per
se. It is, of course, important to note whether basidia are two-spored or fourspored, and whether both kinds occur on one basidiocarp. This may affect
spore size, as spores on two-spored basidia tend to be larger than on fourspored, even in the same species. Also, the feature of two-sporedness, at least
in some agarics, is very constant and can be used as a convenient character
for identification. Its taxonomic value, however, rests on whether or not it
can be correlated with more basic features. We made a preliminary attempt
to count chromosomes in a number of species, but the few figures available
and the small size of the chromosomes were such that we decided to make
this the subject of a later special study.
Cystidia. Scattered among the basidia on the sides, on the edges of the
gills, or on the pileus, cystidia may be present. In Singer (1962: 660) the
statement is made under Crepidotus: "cystidia none on the sides of the lamellae but always present on the edges (cheilocystidia)." Pilat (1948) also states
that in Crepidotus cystidia are absent on the sides of the lamellae. Our studies
contradict these statements. We have found cheilocystidia to be present in
all species except C. albidus and C. aquosus. We have found pleurocystidia in
a number of species and have used their presence to help define infrageneric
taxa (see Figs. 44, 51, 54, 67, 70, 72, 112, 117, 121, 125, and others). We
have known for over twenty years that this situation existed, but have never
published on it. In Crepidotus these structures are not always as conspicuous
as in many genera of agarics, nevertheless they are present. Our use of this
feature is in line with present day treatments in other genera. In Crepidotus,
as in Tricholomopsis, the morphological differences between the cystidia of the
various species is not great and hence not of major taxonomic significance.
Cheilocystidia. These structures are more diverse in form than the pleurocystidia, as the illustrations (see drawings) readily show. They furnish a
number of the characters on which species are distinguished. One of the fea