GROWTH OF CRUSTOSE LICHENS: A REVIEW
Article first published online: 1 MAR 2010
© The authors 2010 Journal compilation © 2010 Swedish Society for Anthropology and Geography
Geografiska Annaler: Series A, Physical Geography
Special Issue: Lichenometry in Subpolar Environments
Volume 92, Issue 1, pages 3–17, March 2010
How to Cite
ARMSTRONG, R. and BRADWELL, T. (2010), GROWTH OF CRUSTOSE LICHENS: A REVIEW. Geografiska Annaler: Series A, Physical Geography, 92: 3–17. doi: 10.1111/j.1468-0459.2010.00374.x
- Issue published online: 1 MAR 2010
- Article first published online: 1 MAR 2010
- Manuscript received July 2009 revised and accepted July 2009.
- radial growth rate;
- thallus development;
- growth curve;
Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (lichenometry). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development; 2) radial growth rates (RGR, mm yr−1); 3) the growth rate–size curve; and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenized fungal hypothallus. Recent data suggest that ‘primary’ areolae may develop from free-living algal cells on the substratum while ‘secondary’ areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the ‘asymptotic’ type of curve recorded in foliose and placodioid species; the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature ‘reproductive’ areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments.