ry period can cause them to become dormant until the next rainfall. Miniscule mineral particles that are carried by the wind during wet conditions are dissolved and absorbed by the lichen.
Lichens produce their own food using sunlight energy and do not feed on the tree bark. The lichen bodies are attached to the outer tree bark and remain on the surface. Their rhizines typically do not penetrate deep enough into the inner bark, and cause no harm to the trees they inhabit.
In contrast, certain fungi operating independently outside a lichen body will penetrate tree wounds or dead wood and feed on the host plant. The filaments of the fungal body will reside inside the tree tissue with only the fruiting bodies visible on the surface.
Lichens are often found on tree trunks, branches and twigs as the bark provides a stable place to reside to collect needed sunlight, rainwater and materials from the air. They grow on healthy trees, as well as stressed or otherwise unhealthy ones. The appearance of colorful organisms growing on the bark of trees or shrubs in the landscape sometimes causes concern for the homeowner. Homeowners may find lichens mysterious and incorrectly associate them as the cause of plant diseases or misidentify them as a type of moss.
Many lichens are more evident on stressed or old tree trunks and branches giving the appearance of a "cause and effect" association with disease and decay. The primary reason for their more likely presence on those trees and branches with reduced or partial foliation is the resulting increase in available sunlight. The bark of a healthy tree continues to expand and slough off with the growth of the tree. The bark of an older or stressed tree may become more brittle with more cracks and uneven surfaces permitting lichens to attach themselves more readily. As bark ages, it changes in chemistry, texture, and ability to retain water, thereby influencing the type of lichen capable of living there.
While fungi-within-a-lichen associations do not harm trees, some fungi outside of a lichen relationship can and do penetrate damaged or dead wood tissue and commence the decomposition of the tree. Fungi are one of the few living organisms that can break down all of the substances in wood tissue and are essential in nature in clearing away fallen tree trunks and in depositing the remaining material into the ground in the forest. A diseased or stressed tree can have both lichen and separate fungal organisms growing on the same dead branch or portion of the tree. In that case, the homeowner or tree expert may need to prune away the dead tissue for the benefit of the remaining plant. In making these types of decisions, homeowners need to understand the unique nature of lichen and the differences between those fungi within a lichen symbiotic relationship and other fungi operating separately.
Lichens do not conform precisely to the usual biological classification categories as they are composed of two or more types of organism living within a single body. Some previous classifications have been modified by recent DNA studies of lichens. The lichen’s appearance and structure are largely determined by the genetic makeup of the fungus that is generally considered the dominant organism. The lichen genus name is normally the same as the specific fungal name, while the species name is descriptive of the resulting dual organism in Latin.
Lichen identification most often is determined by the descriptive appearance, size, shape and color of the lichen body and the reproductive characteristics. Lichens are placed in groups based on their body forms and features. The three main body groupings are crustose (crust-like,), foliose (leaf-like, seen above), and fruticose (tube or beard-like strands).
The various chemicals produced by lichens are also identifying markers. Lichens also can be somewhat differentiated by the specific type of habitat where they live, such as rock, soil or trees, as well as their geographic distribution. While a 10X hand lens is essential in studying lichen specimens, microscopic examin