Public Description of Rhizocarpon geographicum (L.) DC.

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Name: Rhizocarpon geographicum (L.) DC.
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 (Latest review: 2012-03-12 18:44:15 CET (+0100) by jason)

Taxonomic Classification:

Domain: Eukarya
Kingdom: Fungi
Phylum: Ascomycota
Class: Lecanoromycetes
Order: Rhizocarpales
Family: Rhizocarpaceae


General Description:

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.


Diagnostic Description:

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?)


Distribution:

Cosmopolitan.


Habitat:

Sunny, exposed, non-calcareous rocks, generally in mountains (1000-3720 m).


Look Alikes:

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

Uses:

Commonly used in lichenometry to date exposed rock surfaces.


References:

Armstrong, R.A. 2011. The biology of the crustose lichen Rhizocarpon geographicum. Symbiosis 55: 53-67. [An interesting study of the biology of this species, especially as relates to growth rates for use in lichenometry.]


Notes:

According to Schoch et al. 2009, this may be the most basal lineage in the Lecanoromycetidae.


Description author: Jason Hollinger (Request Authorship Credit)
Description editor: Nathan Wilson


Created: 2008-10-23 23:32:21 CEST (+0200) by Jason Hollinger (jason)
Last modified: 2012-03-12 18:44:15 CET (+0100) by Jason Hollinger (jason)
Viewed: 62 times, last viewed: 2016-09-19 10:39:02 CEST (+0200)