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This work presents the genetic and morphological diversity of small <em>Cortinarius</em> subgenus <em>Telamonia</em> species found from moist <em>Salix</em> thickets in Finland. The boreal fungi were compared with several type and other specimens from the alpine zone or similar habitats from the temperate zone. The boreal and alpine zones had many common species: nearly all boreal species grew in the alpine zone with dwarf <em>Salix</em>. The species often had wide distributions, extending to North America. The genetic analyses consisted of ITS and RPB2 sequences. Both genetic and morphological variation was high. The species formed complexes, where the boundaries among species were often obscure. Very close sibling species were delimited based on differences at the same sites. Twenty-three boreal species were recognized. Four of them are described here as new: <em>C. paulus</em> and <em>C. paululus</em> as sibling species to <em>C. pauperculus</em> J.Favre, <em>C. rusticelloides</em> as a sibling species to <em>C. rusticellus</em> J.Favre, and <em>C. vienoi</em> as a sibling species to <em>C. perzonatus</em> Reumaux. <em>Cortinarius sagarum</em>, a sibling species to <em>C. comatus</em> J.Favre and <em>C. vulpicolor</em> M.M.Moser & McKnight, is described as new from arctic-alpine zones.

The diversity and characteristics of species within Inocybe section Inocybe Singer were investigated in Finland. As a result, 11 species are described here as new: Inocybe acutoides,

Distributions of leaf galls and offspring performance of two Pontania sawfly species were explored in individual willows of the subarctic Salix caprea–starkeana hybrid complex. The more common sawfly, an undescribed species near the dolichura group (P1), had the highest gall numbers in trees with long shoots both in S. caprea and hybrids. While numbers were high on vigorously growing hybrids, offspring of P1 were aborted significantly more often on hybrids than on pure hosts. Further, non‐aborted galls were smaller on hybrids. Fast shoot growth may be important for P1 sawflies, because females oviposit early in summer and larvae develop rapidly compared with the other species, Pontania pedunculi (P2). Distributions of P2 galls were related to tree height and not to shoot length in both parental and hybrid groups of willows. Like P1, also P2 offspring were frequently aborted on hybrids, but not significantly more often than on pure hosts, and P2 galls were equally large among the host groups. Survival of both species was related to abortion rates, while larvae were parasitized equally in all host groups. This study demonstrates that the significance of plant vigor may vary even for closely related galling sawflies exploiting the same hosts, or for the same species on different host plants. Vigorous growth may mislead gallers to oviposit on suboptimal plants.

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