Alternaria and Macrosporium are closely allied genera
of the Hyphomyctaceae, both being included in the section
Dictyosporae of the Dematicae. They are differentiated by
their methods of conidia-formation. In Macrosporium a
conidiophore bears at its apex a single conidium, which attains
its full size, matures, and finally becomes detached. In
the case of Alternaria, the conidiophore produces at its apex
a chain of conidia, each of which is morphologically identical
with the single conidium of Macrosporiurn. This chain of
conidia produced by Alternaria eventually becomes broken
up into individuals which cannot be distinguished from a detached
conidium of Macrosporimn. It is, therefore, only
possible to refer a particular species to one or other of
these two genera when the manner in which the conidia
are produced has been determined. Consequently, many
species have been incorrectly placed, owing to inaccurate
observations on the conidia and method of conidia-formation.
The abundance of species apparently placed indiscriminately
in either genus and having synonyms in the
complementary genus is evidence of the fact that these two
genera are much confused. Thus Alternaria solani,
Sorauer= Macrosporium solani, E. & M
