Map Lichen
The map lichen (Rhizocarpon geographicum) is a bright yellow-green crust lichen with black borders that grows on bare rock in mountains and polar regions. The patches look like countries on a map.
The map lichen (Rhizocarpon geographicum) is a bright yellow-green crust lichen with black borders that grows on bare rock in mountains and polar regions. The patches look like countries on a map.
🧬 Field Guide Specimen: Open Map Lichen in the CRV Science Field Guide to log the specimen, see its place among the Opisthokonta lineages in the Cladogram Explorer, and test your recall in the Red List conservation game.
Lichenometry: A Clock From a Crust
Map lichens grow very slowly, in the order of a fraction of a millimeter a year, and the largest thallus on a rock gives a minimum age for when it was exposed. Scientists use the sizes of these lichens to date glacier moraines, rockfalls and gravestones.
Limits of the Method
Growth rates vary with climate and place, so the method must be calibrated locally with surfaces of known age. The "species" is also a complex of several look-alike species.
Pioneers on Rock
Crustose lichens slowly dissolve rock surfaces with acids and begin the formation of soil. See Common Orange Lichen.
Map Lichen at a Glance
| Property | Value |
|---|---|
| Scientific name | Rhizocarpon geographicum |
| Kingdom | Fungi |
| Phylum | Fungi |
| Class | Lecanoromycetes |
| Order | Rhizocarpales |
| Family | Rhizocarpaceae |
| Field Guide group | Opisthokonta: Fungi (True Fungi & Lichens) |
| Diagnostic feature (Field Guide) | Yellow-green patches outlined in black on bare rock, like countries on a map; grows less than 1 mm per year. |
| Growth form | Crustose lichen |
| Use | Lichenometric dating |