Mycorrhizae, the symbioses between fungi and plant roots, are nearly universal in terrestrial plants and can be classified into two major types: endomycorrhizae and ectomycorrhizae. About four-fifths of all land plants form endomycorrhizae, whereas several groups of trees and shrubs, notably Pinaceae, some Cupressaceae, Fagaceae, Betulaceae, Salicaceae, Dipterocarpaceae, and most Myrtaceae form ectomycorrhizae. Among legumes, Papilionoideae and Mimosoideae have endomycorrhizae and usually form bacterial nodules. The members of the third subfamily, Caesalpinioideae, rarely form nodules, and one of the included groups, the two large, pantropical, closely related tribes Amherstieae and Detarieae, regularly form ectomycorrhizae. Nodules and ectomycorrhizae may well be alternative means of supplying organic nitrogen to the plants that form them.
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