Phoma is a fungal genus classified within the molds with over 200 known species, found all over the world. These fungi classically live in the soil, and they may periodically infest plants by attaching themselves to the roots of the plants and colonizing the plant from there. It can be difficult to firmly identify fungi in the Phoma genus, and to narrow down the identification to species, and these fungi may occasionally be confused with examples from other genera. This is a common problem with molds and fungi, as the differences between species can be too subtle to identify in the field or without the proper equipment.
These fungi reproduce asexually, and they are what is known as dematiaceous, meaning that they have melanin in their cell walls. This causes Phoma to appear dark in color, especially when they are massed in a large colony. A colony can spread very rapidly under the right conditions, classically growing into the substrate so that it can be difficult to separate the fungus from the material it grows on. Phoma is sometimes seen indoors on walls, where it can be very destructive.
A classic colony has a velvety texture which can be slightly powdery, depending on the species. It may be white to gray with pink, yellow, and reddish purple colorations. Phoma mold produces distinctively rounded fruiting bodies which can be clearly seen under a microscope, and the spores are single celled. Left unchecked, Phoma will happily spread to cover an area.
In plants, Phoma species are common pathogens. The fungi can cause a condition known as Phoma blight, characterized by a withering and fading of the leaves of the plant. The blight will eventually kill the plant, and it can spread to other plants and trees in the vicinity. Phoma blight can be a very serious problem for nurseries, as the fungus may spread across a wide area before people realize what the problem is, and it will happily lie in wait in the soil until plants are returned to the area, causing a recurrence of the initial blight.
In humans, exposure to some Phoma species can trigger mold allergies, especially when the fungus grows indoors. Respiratory infections can also occur along with phaeohyphomycosis, a subcutaneous skin infection which causes discoloration of the skin as the fungus grows inside the layers of skin. Antifungal drugs and debridement of the site are used to treat this skin infection. Animals can also develop phaeohyphomycosis infections.