The biology of the lichen Rhizocarpon geographicum: symbionts, growth, ecology, and lichenometry

Richard A. Armstrong

Research output: Chapter in Book/Published conference outputChapter (peer-reviewed)peer-review


Rhizocarpon geographicum (L.) DC. is one of the most widely distributed species of crustose lichens. This unusual organism comprises yellow-green ‘areolae’ that contain the algal symbiont which develop and grow on the surface of a non-lichenized, fungal ‘hypothallus’ that extends beyond the margin of the areolae to form a marginal ring. This species grows exceptionally slowly with annual radial growth rates (RGR) as low as 0.07 mm yr-1 and its considerable longevity has been exploited by geologists in the development of methods of dating the age of exposure of rock surfaces and glacial moraines (‘lichenometry’). Recent research has established some aspects of the basic biology of this important and interesting organism. This chapter describes the general structure of R. geographicum, how the areolae and hypothallus develop, why the lichen grows so slowly, the growth rate-size curve, and some aspects of the ecology of R. geographicum including whether the lichen can inhibit the growth of its neighbours by chemical means (‘allelopathy’). Finally, the importance of R. geographicum in direct and indirect lichenometry is reviewed.
Original languageEnglish
Title of host publicationAdvances in Medicine and Biology
EditorsLeon V. Berhardt
PublisherNova science
Number of pages19
ISBN (Print)9781612097961
Publication statusPublished - 1 Feb 2012

Publication series

NameAdvances in Medicine and Biology
PublisherNova Science Publishers


  • hizocarpon geographicum (L.) DC.
  • crustose lichens
  • lichenometry


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