Common Name: Golden Map Lichen
Bright lemon-yellow to greenish-yellow tiled crustose lichen growing over a thin unlichenized black prothallus on exposed granite and other siliceous rocks, especially in mountains.
Regularity: Regularly occurring
Regularity: Regularly occurring
THALLUS: pale to bright lemon yellow to greenish-yellow, areolate crust, underlain by thin black prothallus visible around the margins and between areolae
APOTHECIA: black inset discose apothecia, often angular like areoles
SPORES: brown, muriform, 20-36 × 10-20 µm
CHEMISTRY: cortex UV+y (rhizocarpic acid major), medulla PD+ yellow (psoromic acid major), rarely C+ fleeting pink/red (gyrophoric acid in cortex? or medulla?)
There are severa other yellow Rhizocarpon species:
|R. macrosporum||identical except for spore size (32-60 × 15-22 µm), less common|
|R. lecanorinum||also has brown muriform spores, crescent-shaped areoles around some apothecia, epihymenium K- or K+ green instead of K+ violet or purple|
|others||spores 2-celled and medulla K/I- in section (instead of blue)|
Some other genera that have yellow-and-black crustose thalli:
|Acarospora||apothecia brownish to yellowish, many spores per ascus, areoles often round or subsquamulose, rarely angular, no black prothallus|
|Pleopsidium||apothecia brownish to yellowish, areoles elongate into distinct short lobes at margin, no prothallus|
|Dimelaena oreina||very pale, distinctly radiating lobes at margin, apothecia not black|
|Caloplaca||yellow to orange, pigment K+ wine red, apothecia not black (in orange species)|
|Candelina||apothecia orange, distinctly lobate around margin, no prothallus|
Sunny, exposed, non-calcareous rocks, generally in mountains (1000-3720 m).
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
Rounded National Status Rank: NNR - Unranked
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: This lichen occurs throughout most of Canada and the western U.S., excluding the interior basin, and in the southern Appalachians and New England. This species typically grows in exposed arctic and alpine habitats on siliceous rocks.
Relevance to Humans and Ecosystems
Commonly used in lichenometry to date exposed rock surfaces.
Rhizocarpon geographicum (the map lichen) is a species of lichen, which grows on rocks in mountainous areas of low air pollution. Each lichen is a flat patch bordered by a black line of spores. These patches grow adjacent to each other, leading to the appearance of a map or a patchwork field.
Map lichen is a lichen widely used by climatologists in determining the relative age of deposits, e.g. moraine systems, thus revealing evidence of glacial advances. The process is termed lichenometry.
Lichenometry is based on the assumption that the largest lichen growing on a rock is the oldest individual. If the growth rate is known, the maximum lichen size will give a minimum age for when this rock was deposited.
Growth rates for different areas and species can be obtained by measuring maximum lichen sizes on substrates of known age, such as gravestones, historic or prehistoric rock buildings, or moraines of known age (e.g. those deposited during the Little Ice Age).
This lichen species is broadly distributed and may be found in most cold areas with exposed rock surfaces. The North American range includes the Sierra Nevada and northern Boreal forests of Canada, Greenland, Iceland Fennoscandia and Siberia. In the tropics it only occurs at high altitudes such as the Andes of Peru and Colombia. Further south the Map lichen is found broadly across Patagonia, in the Falkland Islands, the sub Antarctic islands and the Antarctic Peninsula.
In Britain it can be found commonly growing on hard siliceous rocks, especially in upland regions. Its range covers virtually all of Scotland, much of North West England, and other upland areas in much of the rest of England, Wales and Ireland too. 
In an experiment, this lichen species was placed in a capsule and launched into space. The capsule was opened, exposing the lichen to space conditions for 10 days before being brought back down to Earth, where it showed minimal changes or damage.
- Tracy Irwin Storer, Robert Leslie Usinger and David Lukas. 2004. Sierra Nevada Natural History, 2nd ed, University of California Press, ISBN 0-520-24096-0, ISBN 978-0-520-24096-4, 439 pages
- C. Michael Hogan. (2008) Black Spruce: Picea mariana, GlobalTwitcher.com, ed. Nicklas Stromberg
- Global Biodiversity Information Facility
- Frank Dobson. 1979. Lichens, An Illustrated Guide The Richmond Publishing Co Ltd, ISBN 0-85546-203-5, page 244
- de la Torre, Rosa; Leopoldo G. Sancho, Gerda Horneck, Asunción de los Ríos, Jacek Wierzchos, Karen Olsson-Francis, Charles S. Cockell, Petra Rettberg, Thomas Berger, Jean-Pierre P. de Vera (August 2010). "Survival of lichens and bacteria exposed to outer space conditions – Results of the Lithopanspermia experiments". Icarus 208 (2): 735–748. doi:10.1016/j.icarus.2010.03.010. ISSN 0019-1035.
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