Relationships within Timmia, especially within T. austriaca Hedw. (Musci, Timmiaceae)

Within the moss genus Timmia, three or four sections have been suggested based on morphology. Earlier studies conflicted in suggesting that T. austriaca Hedw. either displays limited phylogeographical structure or includes large molecular variation with potential for geographical structure.

Relationships within Timmia were inferred from variation in the nuclear 26S and plastid atpB–rbcL and trnL–trnF. New sequences were generated for 64 specimens of T. austriaca. For other Timmia species, sequences came primarily from earlier studies or GenBank.

Timmia includes two main, well-supported molecular lineages. Within T. austriaca, four arctic or subarctic specimens resolved in a small-lineage sister to all other specimens.

Recognition of two sections is suggested: Timmia Hedw. sect. Timmia (syn. sect. Timmiaurea Brassard; syn. sect. Sphaerocarpa Y.Jia & Yang Liu bis) and sect. Norvegica Brassard. Timmia fossils, including T. austriaca, were deposited at least 3 Myr BP in northernmost North America under a milder climate than presently in that area. It is theorised that plants of the small T. austriaca lineage evolved adaptations to survive only under cold conditions, when the Arctic was gradually cooling. Timmia austriaca disperses easily, and because the numerous temperate region samples studied included no representatives of the northern lineage, the restricted distribution of this lineage is suggested to have resulted from adaptation to cold environments. In situ survival of T. austriaca in Fennoscandia during the Late Glacial Maximum, as previously theorised, is deemed unlikely due to glacial erosion and submergence of large areas as a result of isostatic depression.