The Suillus mycota of Nepal was studied. Nine species are recognized and described; five of the nine appear to be new species. Additional species were collected, but material was inadequate to describe them completely. Cultures of eight and synthesized ectomycorrhizae of six of the Suillus species are described. Synoptic keys to the basidiocarps and to the cultures are presented. Numerical taxonomic analyses of the cultures generated clusters which paralleled the species concepts developed using basidiocarps and ecology. Each species of Suillus from Nepal is host specific based on basidiocarp formation; all hosts are in the Pinaceae. Field associations are Suillus cf. granulatus, S. cf. placidus, S. sibiricus, and greening-foot Suillus with Pinus wallichiana; queen's Suillus with P. roxburghii; waxy Suillus with P. patula; and S. laricinus, himalayan Suillus, and orange-pored Suillus with Larix himalaica. Mycorrhizal syntheses confirmed that the six Suillus-Pinus relationships are ectomycorrhizal. The Suillus mycota of western Virginia has 12 known species. Three, of the five which are ectomycorrhizal with Pinus strobus, have closely related counterparts in Nepal. These counterparts are ectomycorrhizal with P. wallichiana, a five-needled pine closely related to P. strobus. The existence of these three pairs of similar fungi, associated with similar pines, suggests the possibility of cladogenic speciation in parallel by the pine lineage and by its ectomycorrhizal fungal associates. Boletinellus merulioides forms abundant sclerotia in nature throughout its range in eastern North America. Sclerotia collected in the forest germinated to form mycelial colonies that had the same appearance and microscopic characteristics as colonies derived from basidiocarps. Sclerotia which had overwintered in the forest were viable in the spring. The spatial pattern of B. merulioides sclerotia in a forest was compared with basidiocarp frequency recorded over four years. Both estimates of the spatial pattern coincided, but year-to-year basidiocarp frequency varied greatly. Individual B. merulioides dikaryons formed large perennial patches. Basidiocarp and sclerotial densities were centered around and declined outward from Fraxinus americana trees. Boletinellus merulioides and Fraxinus pennsylvanica did not form ectomycorrhizae when grown together in growth pouches. / Ph. D.