Moulds, mildews, yeasts, mushrooms and puffballs. The fungi are a group of organisms that lack chlorophyll (in other words, they are not photosynthetic) and are usually non-mobile, filamentous and multicellular. Some grow in the ground; others attach themselves to decaying trees and other plants. Fungi obtain their nutrition from decomposing organic matter. Some cause disease; others stabilize sewage and break down solid wastes in composting.