Intrathalline variability of some structural and physical parameters in the lichen genus Lasallia

The intrathalline variability of several physical and anatomical parameters of two lichens, Lasallia hispanica and Lasallia pustulata within the family Umbilicariaceae, was studied. In each thallus three zones or concentric rings were considered: the central zone, which includes the umbilicus, the intermediate zone, and the marginal zone. The study focussed on the thickness of the thallus and its layers, the increase of surface area and volume with hydration, the sample densities in dry and wet states, several stereological parameters (especially the volume and surface density of both symbionts related to each layer and to the thallus as a whole), and the chlorophyll content. Only slight differences were revealed between the two species, but significant intrathalline variation was observed. A marked decrease in the total chlorophyll content coincided with the thickening of the thallus from the periphery to the centre. The chlorophyll content of individual algal cells, however, presented an inverse gradien...