Many lichens present a powdery-looking thallus, usually without apothecia, and gray, green, or bluish color. These species are usually found in bark crevices, where they can sometimes cover large areas. It can be either a crustose thallus covered with soralia, or a leprous thallus composed exclusively of small granules. Determining these lichens requires the use of chemical reagents, microscopic examination, as well as molecular analysis.