A mycorrhizal relationship is the symbiosis between a plant and a fungus. Mycorrhizal fungi initiate these symbiotic relationships by attaching themselves to the roots of a proper plant host. Both the plant and the fungus significantly benefit from this underground interaction. The plant benefits because hyphae act as an extension of the plant’s roots, thus increasing the plant’s absorption of minerals and water. The fungus benefits because the plant delivers photosynthetic products (carbohydrates) directly into the cell walls of the fungus. Therefore, when a mycorrhizal relationship forms, both the plant and the fungus experiences an increase in growth. In total, approximately 90% of all vascular land plants have acquired mycorrhizal relationships. Some of these relationships are a lot more common than you may expect.
Ectomycorrhizae & Trees
Ectomycorrhizal fungi initiate their symbiotic relationships by forming thin sheaths of hyphae around the plants’ roots — this structure is called a “hartig net.” Ectomycorrhizae only associate with approximately 2% of plant species. Despite this lack of diverse associations, some of the most common plants prefer ectomycorrhizal relationships. Many genera of evergreen coniferous trees (Pinaceae family) require ectomycorrhizae to grow, including pine, fir, spruce, and hemlock. A number of leaf-bearing trees also depend on ectomycorrhizal fungi, such as oak, hickory, beech, and alder.
Ectomycorrhizae produce fruiting bodies (mushrooms) after forming a mycorrhizal relationship. So, what types of ectomycorrhizal mushrooms can we expect to be growing in association with these trees? Well, there are way too many fungi species to name here — but, I’ll discuss some of the most common genera…
Perhaps, Russula is the most common ectomycorrhizal genus in the world. Worldwide, there are approximately 750 species of Russula. Different species of Russula create mycorrhizal relationships with different plants. For example: Russula emetica prefers pine trees as symbiotic hosts, while Russula brevipes prefer relationships with firs, spruces, and hemlocks. You can observe these different types of associations on your own when you’re out foraging. If you walk into any forest during the warmer seasons, there is a very strong chance you’ll find some Russulas.
The Russulaceae family makes-up a large majority of common ectomycorrhizal mushrooms. The Lactarius genus is a member of this family, making it a close cousin of the Russulas. I have created a short video detailing the essential facts of Lactarius mushrooms…
The Underworld of Endomycorrhizae
Just like ectomycorrhizae, endomycorrhizal fungi form symbiotic relationships with plants. However, these two types of mycorrhizae are very different from each other. Unlike ectomycorrhizae, endomycorrhizae penetrate the cortical cells of the plant host. Endomycorrhizae are often called arbuscular mycorrhiza, because they form arbuscules (and vesicles) within the roots of the host plant.
While ectomycorrhizae only associate with ~2% of plant species, endomycorrhizae associate with approximately 90% of plant species. Surprisingly, barely any of these fungi produce mushrooms. Instead, arbuscules focus their energy of delivering water, sulfur, nitrogen, phosphorus, and other micronutrients to the plant host. Since endomycorrhizae effectively deliver an abundance of nutrients, most plants greatly benefit from these associations:
As of recently, it’s becoming increasingly popular to introduce endomycorrhizal species to garden beds. Research has shown that introducing arbuscular fungi into gardens significantly improves the overall yield of fruits and vegetables.
Considering that arbuscular mycorrhiza are hidden underground, there is great uncertainty about their taxonomy, in terms of species identification. If you’d like to conduct your own research into specific endomycorrhizae, check out these families: Glomeraceae, Claroideoglomeraceae, Archaeosporales, Diversisporaceae, and Paraglomeraceae.