Lobe growth and marginal zonation in crustose lichens
Lobes of Xanthoria elegans are shown to be engulfed by more rapidly growing neighbouring lobes, thereafter ceasing to grow, and the rate of lobe engulfment increases with thallus age. Similarly, growth can cease when lobes of adjacent thalli meet. Mature central areas of eroded thalli may regenerate lobes and resume growth. In Buellia coniops, B. russa and Caloplaca cirrochrooides, peripheral concentric zonation does not always correspond to a single year's growth, and one zonation effect is correlated with an unusually severe winter.