More info!
https://sciweb.nybg.org/Science2/hcol/mycorrhizae.asp.html

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Mycorrhizae (singular: mycorrhiza) are mutualisms formed between fungi and plant roots. The importance of mycorrhizae cannot be overstated; it has been suggested that as many as 95% of all the world's plant species form mycorrhizal relationships with fungi and that in the majority of cases the plant would not survive without them. Mycorrhizae have existed for a very long time and can be demonstrated in the fossilized roots of some of the earliest land plants. They can be found in plants growing in habitats ranging from humid to dry tropics all the way to the far north and south. Some scientists have suggested that plants were only able to move on to land when they had developed mycorrhizal relationships with fungi.

Mycorrhizae are considered to be a mutualistic relationship because both organisms benefit. The fungus receives the products of photosynthesis from the plant and is thus freed from the necesity of finding its own sources of energy. At the same time the fungus grows out into the soil and retrieves nutrients, especially phosphorus and nitrogen, and passes these back to the plant. Numerous experiments have shown that plants without mycorrhizae cannot cope as well with low mineral levels as those that have mycorrhizae.

It is generally believed that mycorrhizae have been re-invented many times over the history of land plants. Many different groups of fungi are involved and the form of the actual fungus-root interface, the mycorrhiza itself, varies greatly. Scientists recognize several distinct types of mycorrhizae and can relate these to particular groups of plants and fungi. The most thoroughly studied of these types are arbuscular mycorrhizae, ectomycorrhizae, ericoid mycorrhizae, arbutoid mycorrhizae and orchid mycorrhizae

Arbuscular mycorrhizae

Arbuscular mycorrhizae (often called AM) are the most common and widespread of all mycorrhizae and are found in as many as 85%-90% of the world's plant species.  Further info here, 

http://website.nbm-mnb.ca/mycologywebpages/NaturalHistoryOfFungi/Mycorrhizae.html

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Ectomycorrhizas

Ectomycorrhizas (sometimes termed ectotrophic mycorrhizas) are characteristic of many trees in the cooler parts of the world - for example pines, spruces, firs, oaks, birches in the Northern Hemisphere and eucalypts in Australia. However, some trees (e.g. willows) can have both ectomycorrhizas and arbuscular mycorrhizas, and most tropical trees have only arbuscular mycorrhizas.

The fungi involved are mainly Ascomycota and Basidiomycota, including many that produce the characteristic toadstools of the forest floor (Figures A-C below). Most of these fungi can be grown in laboratory culture but, unlike the wood-rotting fungi, they are poor degraders of cellulose and other plant wall materials. So they gain most of their sugars from the living plant roots in natural conditions.

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A. Rings of toadstools of mycorrhizal fungi (Hebeloma and Lactarius species) around the base of a birch tree. 

B. Fruitbody of Lactarius. The gills of this toadstool were cut to show that the fungus exudes a milky fluid when the tissues are damaged - hence the name 'Lactarius'. 

C. Fruitbody of Amanita muscaria (the 'fly agaric') which is a typical mycorrhizal fungus of birches but also can be found on some other trees.

D, E. Mycorrhizal roots. In ectomycorrhizas the terminal branches of the root system are highly modified - the roots are short and stumpy, covered with a mantle (sheath) of fungal tissue (the creamy-white root surface in D), and there are few or no root hairs. The fungus takes over the normal nutrient-absorbing role of the root hairs. In E the fungal mantle is less conspicuous, but the fuzzy appearance of the roots is due to many fungal hyphae growing from the mantle into the soil. Such roots are seen easily if the undecomposed, surface litter is scaped away from the forest floor to reveal the decomposing litter containing a mass of mycorrhizas and their fungal networks.

F. Cross-section of a pine mycorrhiza, showing the substantial fungal sheath that encases the root (labelled 's')..

G. Higher magnification of the sheath (left side) composed of a tightly packed fungal 'tissue'. From the inner side of the sheath, the fungus grows between the root cortical cells, forming a network termed the Hartig net (Hn). The sections in F and G were stained to show phenolic compounds (red) that often are formed in pine roots in response to mycorrhizal infection. They might have a role in limiting the fungal invasion of the tissues.

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Arbuscular mycorrhizas

Arbuscular mycorrhizas are found on the vast majority of wild and crop plants, with an important role in mineral nutrient uptake and sometimes in protecting against drought or pathogenic attack. Structures resembling those of the present-day AM fungi have been found in fossils of primitive pteridophytes of the Devonian period. It is thought that these fungi colonised the earliest land plants and that mycorrhizal associations could have been essential for development of the land flora.

The fungi involved are members of the zygomycota (related to Mucor). They are classified currently in six genera (Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora) and they seem to be obligate symbionts: none of them can be grown in axenic culture, i.e. in the absence of their hosts. 

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