Wart lichens (genus Pertusaria) are warty pale gray or whitish crustose lichens. Although some species have cuplike apothecia (spore-bearing organs), this genus is especially noted for having the apothecia covered by wartlike nubbins, which gradually erode, creating a hole (or holes) from which the spores can exit. Globally, there are more than 500 species; Missouri has about 18.
Like other crustose lichens, wart lichens are tightly attached to the substrate they grow on. They often look like a patch of old, weathered paint. In this genus, the surface may look especially cracked, lumpy, or bumpy.
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. Many of these are gray or pale and have reproductive structures that appear warty, pimply, or nubby — not just the ones in genus Pertusaria. These are some of the more challenging species for amateurs to identify.
Lichens begin as tiny spots but may grow to cover several square inches. Groups may coalesce to cover large areas.
Statewide.
Habitat and Conservation
Different species of lichens have different preferred habitats. Look for wart lichens on tree trunks (especially ones with smooth, tight bark such as hickories), or sometimes on rocks.
The rock wart lichen (Pertusaria plitiana) is one of the few members of this genus commonly found on rocks, especially acidic or neutral rocks such as sandstone. Missouri's approximately 17 other species in the genus mostly live on tree trunks.
Status
Lichens do not harm the trees they live upon.
Human Connections
Wart lichens probably won’t win many beauty awards, but overall, they contribute to the interesting textures of tree trunks and make the woods more interesting.
Ecosystem Connections
Many animals, including beetles, moths, treefrogs, lizards, and birds, have camouflage coloration that blends with these and other lichens that live on trees.
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.