The ubiquitous ectomycorrhizal associations usually have classic features such as a well-developed fungal mantle that interfaces with the soil matrix, and a Hartig net, a complex of labyrinthic intercellular hyphae responsible for mutual nutrient exchange. Epidermal and cortical Hartig net development occurs in angiosperm and gymnosperm host roots, respectively. Monotropa and Pterospora species exhibit a mycoheterotrophic achlorophyllous habit that has attracted the interest of plant biologists. In addition to typical mantle and Hartig net, these mycorrhizas possess unique epidermal fungal pegs that are also considered sites for metabolite exchanges. The fungal relationship of monotropoid roots suggests an epiparasitism of tree roots via shared mycelia. The Pyrolaceae possess features considered intermediate between ecto- and ericoid mycorrhizas and have been classified as arbutoid (including pyroloid) mycorrhizas. They are distinguished by lacking a mantle, but having a Hartig net plus elaborated intra-epidermal hyphal complexes. The symbiosis of these two mycorrhiza groups include associations with a variety of fungi that can potentially form linkages with other hosts in the plant community. The mycotrophy and structure of two monotropoid species (Monotropa uniflora L. and Pterospora andromedea Nutt.) from central British Columbia, as well as an arbutoid plant (Pyrola rotundifolia L.) from Quebec, are examined using morphological and molecular methods, in combination with light microscopy, scanning electron microscopy and confocal laser scanning microscopy. The morphology and structure of Monotropa and Pterospora mycorrhizas are described, and the molecular diversity of the fungi associated with their roots explored. With respect to Pyrola, key structural features will be described and compared to ectomycorrhizal systems.

Key words: Monotropa, mycorrhiza, Pterospora, Pyrola, structure