The genus Comatricha is very similar to the genus Stemonitis. Despite their similarity, one way they can be distinguished from each other is by surface net characteristics. Even in the species within the genus Comatricha which develop capillitium that are extensively anastomosed near the surface of the sporangia (Comatricha typhoides and Comatricha laxa), there is no surface net. On the other hand, a surface net is almost always present in Stemonitis sporangia.
This is a book except from Martin, Alexopoulos, Farr (1983). It includes an original description for separating genus Comatricha from close relatives as well as subsequent modifications of it:
“Even in such species as Comatricha typhoides and C. laxa, where the capillitium is extensively branched and anastomosed near the surface, the lack of a surface net is apparent, whereas it is nearly always present in Stemonitis sporangia, at least in the lower portion, and to a greater extent than the descriptions imply in those species in which it is said to be lacking above. In S. hyperopta, for example, there are often traces of delicate net in the upper part of the sporangium, although the net falls away more quickly than in other species.
Ross (1958b) showed that, in three species of Stemonitis, the capillitium developed both from the columella and from areas within the sporogenous mass and that the net developed just under the surface from loci within the peripheral protoplasm, while in Comatricha typhoides the entire capillitial system arose from the columella. Goodwin (1961) studied three additional species of Comatricha and found that they developed as described by Ross for C. typhoides. This suggests that the presence or absence of a net may be of fundamental significance.
Alexopoulos (1967) stressed the importance of stalk characters in these genera; stalks of Stemonitis and Macbrideola typically are hollow, tubular, and homogenous, while those of Comatricha are filled with an interlaced mass of threadlike strands. Partly on that basis he transferred three of the minute species of Comatricha to Macbrideola.
Hertel (1956) earlier suggested extensive revision of Comatricha, proposing several new genera. His work was reviewed and amplified by Nannenga-Bremekamp (1967). The latter author recognized Paradiachea Hertel essentially as it was originally proposed, to include those species with a persistent peridium. In view of the quantitaive variation of this character among and even within species (Comatricha typhoides, for example), this separation appears superfluous. Nannenga-Bremekamp (1967, 1974) also accepted and substantially modified Paradiacheopsis Hertel, transferring several additional species to that genus, and distributed the residual species of Comatricha among four subgenera: Comatricha, Laxaria Nann.-Brem., Sinuaria Nann.-Brem., and Stemonitopsis Nann.-Brem. The last name was rasied to generic rank in her book (1974) and typified by Stemonitis hyperopta."
This is a book excerpt from Macbride (1922). If offers more history regarding the origin of the genus Comatricha:
“Sporangia cylindric or globose, stipitate; stipe prolonged upward to form more or less extended and tapering columella bearing branches on every side, which by repeated divisions and reunions form the capillitium; ultimate branch-tips free, not supporting a surface net parallel to the peridial wall; peridium evanescent, perhaps sometimes not developed at all.
The genus Comatricha was set off from Stemonitis by the joint effort of Preuss (1851) and Rostafinski (1873-5). Preuss included in his genus, Comatricha, alien forms, and besides failed to give an accurate definition; included, however, in his list some species which have since been known by his generic name.
The distinction between the two genera is almost an artificial one, and species are sometimes arbitrarily assigned to one genus or the other. The diagnosis in any case turns upon the presence or absence of a surface net, formed, in Stemonitis, by the anastomosing of the ultimate divisions of the capillitial branches. In Comatricha the anastomosing is general, from the columella out, and is not specialized at the surface.
Recent attempts to reunite the genera here compared seem to result in no apparent advantage. The genera come very near together, but their separation along the line suggested by Rostafinski remains convenient."
Comatricha nigra is one of the most common species. A partial sequence of the Comatricha nigra voucher AMFD155 small subunit ribosomal RNA gene from GenBank® can be found here DQ903683 2783 bp DNA linear INV 30-OCT-2008 .
Further pictures and info for the genus Comatricha :