Accurate lifespan estimates cannot be obtained from 14C profiles in the crustose lichen Rhizocarpon geographicum (L.) DC.

Radial C-14/C profiles across three individuals of the crustose lichen Rhizocarpon geographicum (L.) DC. have been determined using accelerator mass spectrometry. These data were used to assess whether lifespan estimates can be determined in this species using C-14/C isotope ratio measurements. C-14/C profiles are relatively flat with Delta C-14 values (deviations from the modern radiocarbon standard) for the radial samples displaying a small spread ranging from 130 to 200 per mil. The data are consistent with carbon cycling based on growth patterns involving replacement and fusion of areoles within the thallus as well as or instead of cellular or molecular replacement. Consequently, lifespan estimates cannot be obtained from C-14/C measurements of this species and the Delta C-14 profiles provide no insights into whether the relationship between size and age is linear or curvilinear in this species. (C) 2001 The British Lichen Society.