The Influence of Aspect on the Pattern of Seasonal Growth in the Lichen Parmelia Glabratula Ssp. Fuliginosa (Fr. Ex Duby) Laund

SUMMARY The radial growth of samples of thalli of Parmelia glabratula ssp. fuliginosa were measured in situ on a south‐facing and a northwest‐facing rock surface each month from August 1973 to July 1974. In the periods August to October 1973 and March to July 1974 the radial growth of thalli in the northwest population was greater than in the south population. In the period November 1973 to February 1974 the radial growth of thalli in the south population was greater than in the northwest population. A physiological basis for the differences in seasonal growth in the two populations was suggested. The mean annual radial growth rate (in units of mm/year) was not significantly different in the two populations. However, the variability in radial growth rate between thalli was significantly larger in the northwest than in the south population. These results may be explained by genetic differences between the populations and environmental differences between the rock surfaces.