AbstractSections of the stems and leaf sheaths of North American, European and Asiatic specimens ofTimmia austriaca, T. megapolitanaandT. norvegicawere examined microscopically to discover useful discriminatory characters for identification purposes. The presence or absence of stereids in the sheathing part of the nerve appears to be a valuable taxonomic character for use in determining otherwise doubtful or unidentifiable sterile material of the sectionsTimmia(stereids present) andTimmiaurea(stereids absent). Similarly, the presence of a continuously thickened layer on the adaxial side of the sheathing lamina appears to be distinctive for T. norvegica. The characteristics of the stem seem to be of no taxonomic importance.