The Glomeromycota are unusual and poorly understood organisms. Fungi from this division rarely produce easily visible structures and cannot be grown without a plant host, so investigating them is very difficult. Glomeromycotan fungi are some of the most important fungi on Earth because they form arbuscular mycorrhizas, which provide essential nutrients to the vast majority of terrestrial plants.
arbuscular mycorrhizal fungi
Arbuscular mycorrhizae have been around since plants began to colonize the land and were probably instrumental in that transition. Ectomycorrhizae and ericaceous mycorrhizae evolved during the time of the dinosaurs and were successful because of their ability to extract organic nutrients from the well-defined soil. Orchid mycorrhizae were the last to evolve. This probably happened around the same time as mammal lineages started to diverge. Despite the tens to hundreds of millions of years of symbiosis, coevolution does not appear to play a large role in the evolution of modern mycorrhizal partners.
The Glomeromycota are all fungi which form arbuscular mycorrhizae (AM). Mycorrhizae are a type of mutualism with plants where the fungus gets sugars and gives up hard-to-extract nutrients (especially phosphorous). AM fungi accomplish this by forming structures within the plant’s root cells while not causing a disease reaction. Most land plant species form AM, and only a few families are considered non-mycorrhizal. AM fungi tend to be generalists, colonizing a variety of different plant species. Each plant is usually colonized by multiple AM species. This mycorrhizal network has a variety of different roles in an ecosystem. It supplies nutrients to plants, determines what species make up an ecosystem’s plant community, and allows other plants (like orchids and Indian pipe) to parasitize larger plants via the network. A recent study has also suggested that plants use AM fungi to communicate with their neighboring plants. For more on AM, see FFF#074. Only...