Verrucaria

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Verrucaria is a group of lichen-forming fungi that grow as crusty patches on rocks. They usually crust limestone and other calcareous rocks, but some species live on siliceous rock, bark, or soil. Some Verrucaria are kept dry, while others can tolerate periodic flooding or even permanent submersion in coastal and freshwater areas. There are about 150 accepted species worldwide, making Verrucaria a diverse but taxonomically challenging group because many species look alike and the genus is polyphyletic (its members don’t all come from a single ancestor).

History and name
- The genus was described by German botanist Heinrich Adolph Schrader in 1794.
- The type species is Verrucaria rupestris.
- The name comes from Latin verruca meaning “wart,” plus -aria meaning “belonging to.”

What they look like and how they reproduce
- Verrucaria forms a crust-like thallus that sits on the rock surface. The surface can be continuous, cracked into plates, or covered with tiny warts.
- Colors range from white, green, or grey to brown and black. Some have a pale margin around the edge.
- Reproduction happens with small, dark, flask-shaped fruiting bodies (perithecia) that are often sunken but can stick out of the crust. Inside, eight spores are produced in each sac (asci).
- Asexual reproduction can occur through embedded structures that release simple, rod-shaped spores (conidia).

Where they live
- Most Verrucaria species grow on rock (calcareous or siliceous). A few are found on bark or soil.
- They live in dry places or in spots that flood from time to time, and they are found in coastal and freshwater environments.
- About 16 marine Verrucaria species were known as of 2015.

Taxonomy notes
- The group is very diverse and continues to grow as new species are found. For example, seven new Verrucaria species were described from Finland in 2020, showing that northern Europe still holds many discoveries.
- The genus has included confusing groups with similar features (such as the old “Thelidium group”), which has led to names being uncertain or debated.

In short, Verrucaria is a large, rocky, crust-forming group of lichens found on many rock types and in a range of habitats, from dry lands to the sea, with significant ongoing discoveries and taxonomic complexity.