The biology of the crustose lichen Rhizocarpon geographicum

Richard A. Armstrong

Research output: Contribution to journalArticle

Abstract

The crustose lichen Rhizocarpon geographicum (L.) DC. comprises yellow-green lichenized areolae which develop and grow on the surface of a non-lichenized fungal hypothallus, the latter extending beyond the edge of the areolae to form a marginal ring. The hypothallus advances very slowly and the considerable longevity of R. geographicum, especially in Arctic and Alpine environments, has been exploited by geologists in dating the exposure age of rock surfaces (lichenometry). This review explores various aspects of the biology of R. geographicum including: (1) structure and symbionts, (2) lichenization, (3) development of areolae, (4) radial growth rates (RaGR), (5) growth physiology, (6) changes in RaGR with thallus size (growth ratesize curve), (7) maturity and senescence, and (8) aspects of ecology. Lichenization occurs when fungal hyphae become associated with a compatible species of the alga Trebouxia, commonly found free-living on the substratum. Similarly, 'primary' areolae develop from free-living algal cells trapped by the advancing hypothallus. The shape of the growth rate-size curve of R. geographicum is controversial but may exhibit a phase of decreasing growth in larger thalli. Low rates of translocation of carbohydrate to the hypothallus together with allocation for stress resistance results in very slow RaGR, a low demand for nutrients, hence, the ability of R. geographicum to colonize more extreme environments. Several aspects of the biology of R. geographicum have implications for lichenometry including early development, mortality rates, the shape of the growth-rate size curve, and competition. © The Author(s) 2012.

LanguageEnglish
Pages53-67
Number of pages15
JournalSymbiosis
Volume55
Issue number2
DOIs
Publication statusPublished - Sep 2011

Fingerprint

Rhizocarpon
Lichens
thallus
algae
lichens
Trebouxia
Biological Sciences
Nipples
Growth
stress tolerance
symbionts
hyphae
early development
Arctic region
physiology
rocks
carbohydrates
ecology
nutrients
cells

Keywords

  • rhizocarpon geographicum
  • lichenization
  • primary areolae
  • radial growth rate
  • RaGR
  • growth rate-size curve
  • lichenometry

Cite this

Armstrong, Richard A. / The biology of the crustose lichen Rhizocarpon geographicum. In: Symbiosis. 2011 ; Vol. 55, No. 2. pp. 53-67.
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The biology of the crustose lichen Rhizocarpon geographicum. / Armstrong, Richard A.

In: Symbiosis, Vol. 55, No. 2, 09.2011, p. 53-67.

Research output: Contribution to journalArticle

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