fungus in the scientific sense, means any of a group of simple plants which include mushrooms and similar plants, yeasts, moulds, and the rusts which grow as parasites on crops (such as ergot on rye). Unlike more advanced plants, fungi lack chlorophyll and so can only grow as saprophytes (from dead plants or animals); or as parasites (on living plants, see cuitlacoche); or in a mycorrhizal relationship (symbiosis between fungi and the roots of trees).
Fungi vary in size from single-cell micro-organisms, too small to be seen by the naked eye, to the giant puffball, which may measure 1.5 metres (5') across. Edible fungi, exemplified by the common field mushroom and its cultivated relation, mostly fall between the two extremes.
