A group of aerobic gram-positive organisms that develop rudimentary to branched vegetative filaments. The colonies are small, leathery and have a granular, powdery or velvety appearance due to the aerial mycelium present. Colonies may be white, gray, yellow, orange, pink, coral, red, tan, brown or purple and may produce an earthy odor. They have been isolated from soil, beach sand, house dust, swimming pools, tap water, plants, dust, water, compost, and manure. They cause human infections following inhalation, or by contamination of an area of trauma.