Asta, J./ Letrouit-Galinou, M.-A. 1995: Observations on the early growth of Rhizocarpon geographicum thalli. - Herzogia11: 239-252. [RLL Suppl.] Keywords: LICHENIZED ASCOMYCETES/ THALLUS MORPHOGENESIS/ RHIZOCARPON GEOGRAPHICUM/ FRENCH ALPS/ COLONIZATION
Abstract: Colonization of quartzite boulders by Rhizocarpon geographicum was studied using a synchronic method. The lichen develops in three scenarios according to four major phenomena: formation of primary areolae by hypothallus hyphae, growth and division of these areolae, confluence of primary areolae, and fusion of thalli. The first scenario is characterized by high density germination on the rock, critical development of the hypothallus and frequent fusions of thalli. In the second scenario, fusion of thalli is of minor importance; the thallus growths essentially by means of the hypothallus margin and by aggregation of the new areolae formed upon. In the third scenario, fusion of thalli and formation of new areolae are rare events and development results in small, although old thalli. Though these observations question the theoretical bases of lichenometry, they remain consistent with the methods and application of this science.