Endolithic lichens and conservation: An underestimate question

Abstract

Endolithic lichens are frequent colonizers of monuments but are not easily recognizable because their color is very similar to the rock. Their thalli completely penetrate the stone and weaken the stone structure by altering the substratum. The knowledge of their physiology and ecology is important for the preliminary steps of restoration of monuments. The chapter describes various endolithic lichens growing on monuments and natural outcrops to examine their morphological features and interactions with stone. Six endolithic species—Acrocordia conoidea, Caloplaca sp., Petractis clausa, Rinodina immersa, Verrucaria baldensis, and V. marmorea— were studied. The collecting sites were Sanctuary of Macereto (Macerata, Central Italy) and Trieste Karst (NE, Italy). Different techniques were applied to investigate the samples (lichen + substratum): microscopic investigations of polished cross and thin sections, X-ray diffractometry, micro-diffractometry, and FTIR. The microscopic examination reveals the anatomical characteristics of these lichens that can be subdivided into three layers: an outer layer consisting of densely conglutinated hyphae; a photobiont layer; and an inner layer of loose web of hyphae. These analyses give information about the depth of penetration in the stone, the position of mycobiont and photobiont as compared with stone surface, the morphological aspects of the thallus-substratum interaction, and the damage caused by the lichens into the substratum. According to analyses performed by X-ray diffractometry, microdiffractometry, and FTIR; Endolithic lichens cause the biodeterioration of limestone not only with the penetration of hyphae but also by means of the formation of fruiting bodies (apothecia and perithecia) creating a bio-pitting.