Cobblestone lichens , or cracked lichens, grow flat against their substrate and are textured like lumpy cobblestone streets or old, cracked, blistered paint, or they are broken into sections like the mud of a dried lake. The thallus (main body) of the lichen consists of tiny polygonal, angular patches separated by fissures in the surface that produce an obvious netlike pattern. These polygonal patches vary somewhat in size. The fruiting bodies appear as dark dots on the surface of the thallus. Depending on species, color can range from white to greenish gray to brown to bright yellow. The color usually changes when the lichen is wet.
Globally, this genus has more than 125 species. Missouri has at least 3. The cobblestone lichens are a difficult group for taxonomists, and the scientific names for our species have changed as researchers sort out this group on a continental scale.
- One impressive Missouri cobblestone lichen is often called the gold or golden cobblestone lichen, Acarospora contigua, though its scientific name is in flux. Its cracked surface looks like bright yellow cobblestones. It is a characteristic lichen of Missouri’s sandstone, chert, and igneous glades and cliff faces; these slightly acidic rock habitats are most common in the unglaciated Osage Plains of western/southwestern Missouri.
Cobblestone lichens are a good example of a crustose growth form. Like other crustose lichens, cobblestone lichens are tightly attached to the substrate they grow on. They have no lower surface.
A lichen is an organism that results when a fungus species and an algae species join together. Although the relationship between the fungi and algae is quite intimate and integrated, the lichen that is formed does not much resemble either of the components. Learn more about lichens on their group page.
Similar species: Of Missouri’s approximately 436 species of lichens, about 200 of them are ones with a more or less crustose growth form. Acarospora isn’t the only genus that can look like cracked paint or tiny cobblestones. Among the many others are species of Aspicilia, Caloplaca, Diploschistes, Lecanora, Pertusasria, Verrucaria, and more.
Lichens begin as tiny spots but may grow to cover several square inches. Groups may coalesce to cover large areas.
Different species have different habitat and substrate requirements, so their distributions vary across the state.
Habitat and Conservation
Different species have different preferred habitats. Members of this group of lichens are often seen growing on rock faces, but others are more common on trees, and others on soil.
Of the species that grow on rocks, most grow only on certain types of rocks, such as sandstone, granite, dolomite, limestone, and so on. Since rock types aren't evenly distributed across the state, the various saxicolous (rock-dwelling) lichens occur in different regions in the state, too.
Similarly, lichens that live on trees frequently live only on bark or on bare wood. And often, only certain tree types or bark textures or pH are needed.
Human Connections
Cobblestone lichens are some of the lichens associated with rocks in the sun-baked deserts and in mountaintop tundra habitats. Even in Missouri, what a marvel to see these fascinating, often incredibly colorful life-forms living on rocks and trees, in what would seem unlivable, dry, weather-beaten conditions. One lichen website calls this beauty and wonder “enlichenment,” and we’d have to agree.
Mosses, liverworts, hornworts, and lichens seem rather similar, but these organisms are in very different groups. Mosses, liverworts, and hornworts are small, low plants usually found in damp habitats. Unlike more familiar plants, they lack veinlike structures and do not produce flowers or seeds — instead, they produce spores. Meanwhile, lichens are not plants at all: they are a collection of different fungi that have photosynthetic algae living within their tissues.