The length of the tail is not a reliable diagnostic character for this species, as it is frequently damaged.

The genus includes three species, whose diagnostic key characters often overlap (Mabberley 1997).

Specifically for the Holmiidae are the following diagnostic characters.

The spore print of a mushroom is an important diagnostic character in most handbooks for identifying mushrooms.

The colour of the flowers is not a diagnostic character.

The fruit is often the most important diagnostic character for plants in this family.

However it lacks any clearly diagnostic characters and its affinity is best considered to lie in an unresolved stem group.

A significant diagnostic character is an unusually numerous hooks, which may be as many as 500.

The reliable diagnostic character of M. tatricus is its karyotype.

Its sinuous appearance, with several branches and notches, makes it a diagnostic character for this species.