A group of aerobic gram-positive organisms that develop aerial and vegetative branched filaments. The colonies are small, leathery and have a granular, powdery or velvety appearance due to the aerial mycelium present. Colonies may be white, cream, gray, yellow, red, blue, green or violet and produce an earthy odor. They have been isolated from soil, plants, dust, water, compost, and manure. They cause human infections following inhalation, or by contamination of an area of trauma.