There are people who leave their mark in their field. Without doubt, Pier Luigi Nimis (for the registry office, Pierluigi; for friends, Pier; for family members, Pil; for me and a few colleagues, PL) is such a person. On the threshold of retirement but no less active than ever, Pier Luigi is about to begin a new phase of his life, a life dedicated entirely to science and, in particular, to lichenology.

This Special Issue is dedicated to Professor Pier Luigi Nimis on the occasion of his 70th birthday and retirement. It was our aim to publish papers addressing the three major research fields that Pier Luigi dealt with during his career: systematics and taxonomy, biomonitoring and ecology, and data resources and digitization. The papers in this Special Issue provide a vivid overview of the state of the art in the three research fields, and they reflect on Pier Luigi's outstanding contribution to lichenology. They offer a wide array of different methodologies, from the traditional approaches investigating lichen diversity and taxonomy by means of morpho-anatomical analyses, culture isolations and phylogenetic systematics, to the most modern sequencing techniques, and to the development of computer-aided tools and databases for facilitating lichen identification.

Removing lichen substances from dry lichen thalli using pure acetone is the least detrimental method. Measurements of properties strictly related to the photobiont, such as chlorophyll a fluorescence (ChlaF), are frequently used to verify acetone toxicity but they cannot reveal possible damage accumulated at the whole thallus level. Here, measurements of ChlaF have been integrated with others concerning the status of cell membranes and photobiont population (potassium leakage, malondialdehyde and photosynthetic pigment content). Dry thalli of Flavoparmelia caperata, Parmotrema perlatum and Xanthoria parietina were subjected to sequential acetone washings according to standard protocols. Membrane permeability was assessed before and after the washing treatment, and after a recovery period of 48 hours. Measurements of ChlaF were taken in a parallel experiment. Acetone washings increased potassium leakage in all the species from 3·9 to 6·6 times greater than the control level. After recovery, only P. perlatum returned to the control level. ChlaF was affected only in F. caperata, with a 20% decrease in Fv/Fm which had not fully recovered after 48 hours. There was neither an increase in lipid peroxidation of membranes nor a change in the photosynthetic pigment content. The sensitivity of F. caperata to this method and the impact of the results on its future application are discussed.

The epiphytic lichen Porina pseudohibernica is described as new. It is characterized by a richly isidiate thallus, 7–8(–9)-septate ascospores and the presence of periphyses. It resembles P. hibernica s. str., differing in the size and septation of ascospores, and in the dimensions of the terete, branched isidia. The new species was found fertile at a single site in the Carnic Alps (SE Alps, Italy), but it is also known in a sterile condition from scattered localities in the humid (sub-)montane belt of Slovenia, the Czech Republic and Ukraine, occurring on smooth bark of Fagus and Carpinus. Porina hibernica is restricted to the coastal lowlands of Atlantic Europe, and it prefers rather dry, base-rich bark of Quercus and Ulmus. The characters previously used to segregate the isidiate European Porina into the genus Zamenhofia are also discussed.

The new species Miriquidica invadens Hafellner, Obermayer & Tretiach is described and reported from Austria, Bulgaria, Italy, Switzerland, France and Spain. From a morphological point of view the species belongs to the M. griseoatra group, in which it is, so far, the only constantly lichenicolous taxon. Chemically it is characterized by the regular presence of miriquidic acid, stictic acid, and constictic acid (in variable amounts). It starts its ontogenetic life cycle as an obligate youth parasite on Sporastatia, usually S. polyspora.

Morpho-anatomical treatments of other species of the Miriquidica griseoatra group occurring in Europe, based on the examination of type material, are also presented. According to the characters exhibited by the lectotype of Lecidea contigua var. griseoatra Flot., M. griseoatra (Flot.) Hertel & Rambold is the correct name for a montane species with subdivided areoles and immersed, laterally adnate apothecia with a pigmented hypothecium. Specimens exhibiting this set of characters were usually named M. obnubila auct. According to the characters observed on the lectotype of Lecidea (Biatora) obnubila Th. Fr. & Hellb., M. obnubila (Th. Fr. & Hellb.) Hertel & Rambold is a species with sessile apothecia with a hyaline hypothecium. Lecidea subplumbea Anzi does not constitute a heterotypic synonym of Lecidea griseoatra (Flot.) Schaer. but is the legitimate name at the species level for Miriquidica griseoatra sensu auct., and therefore M. subplumbea (Anzi) Cl. Roux is the correct name for that taxon. Lecidea inserena Nyl. is confirmed as a heterotypic synonym of Lecidea subplumbea Anzi. Lecidea plumbea Garov. ex A. Massal. is an earlier heterotypic synonym of Miriquidica limitata Hertel & Rambold and, therefore, the new combination M. plumbea (Garov. ex A. Massal.) Hafellner, Obermayer & Tretiach is introduced.

Lectotypes are designated for Lecidea contigua var. griseoatra Flot., Lecidea inserena Nyl., Lecidea obnubila Th. Fr. & Hellb., Lecidea plumbea Garov. ex A. Massal., and Lecidea subplumbea Anzi. A key to the taxa of the M. griseoatra-group and other Miriquidica taxa with a grey thallus is provided.

The effects of hydrogen sulphide (H2S) on five lichens with different photobionts, ecology, and tolerance to the pollutant were studied by means of samples exposed in closed chambers containing two known H2S solutions. The H2S concentration in the void volume at equilibrium with the liquid phase was measured by gas chromatography-mass spectrometry, combined with the use of solid phase micro extraction (GC/MS SPME). It was determined as 8 and 28 ppm H2S in the absence of lichen material, and c. 2 and 10 ppm H2S respectively with living lichen material inserted for 8 hours in the exposure chambers. Significant differences in the species-specific emission of chlorophyll a fluorescence (ChlaF) were observed, with a pronounced depression of Fv/Fm already detectable after 2 h exposure at 28 ppm H2S in all the species. The decreased intensity was positively correlated to sample surface and, to a lesser extent, to the species-specific pre-exposure Fv/Fm value. Dark-exposed samples were less affected than light-exposed ones. All four chlorolichens could recover the pre-exposure ChlaF emission after two days in the absence of H2S, both in the light and in the dark, whereas the cyanolichen did not recover when kept in the dark. The results are thoroughly discussed on the basis of the known action mechanisms of H2S on the photosynthetic apparatus of vascular plants and cyanobacteria.

A thorough chemical, molecular and morphological study has been carried out on a problematic group in the genus Lepraria characterized by lobed, granular thalli with a raised rim and a preference for mosses, rocks and mineral soils in exposed, xeric habitats. The material examined was collected in seven countries of the Mediterranean-Macaronesian region, from chalk, carbonate rocks and derived soils (A-thalli), and from siliceous rocks and derived soils (B-thalli). The results of a phylogenetic analysis based on 93 ITS sequences (29 of which newly obtained) support the identification and the segregation of two taxa at species level, provisionally identified as Lepraria isidiata s. lat., (most of the A-thalli), and L. santosii s. lat. (B-thalli plus the remaining A-thalli), as the observed genetic variability is quite high. Three chemotypes were detected in L. isidiata s. lat., and seven in L. santosii s. lat. The two taxa are morphologically well characterized: in L. isidiata s. lat. the thallus is thicker and the propagules larger than in L. santosii s. lat. The first stages of thallus development from single propagules are described in both species. Some critical remarks are made about the increasing use of the species rank for taxa of Lepraria, which are morphologically and genetically scarcely characterized.

Chlorophyll a fluorescence was measured every three months from December 2003 to December 2004 in ten, randomly selected thalli of the epiphytic lichen Punctelia subrudecta (Nyl.) Krog occurring in a deciduous, thermophilous downy oak wood in southern Tuscany (central Italy). In situ measurements were carried out with a photosynthesis yield analyser Mini-PAM (Walz, Effeltrich, Germany) on the same measuring points of 30-minute dark-adapted, fully hydrated thalli. The results show a remarkable seasonal change in Fo, Fm, and Fv/Fm, probably caused by a long-term physiological-structural adaptation of the photobiont to the gradual modification of the climatic conditions of each measurement period and the light regime of the understorey. However, P. subrudecta is also sensitive to rapid changes in microclimatic conditions as the PSII functionality is affected by the light regime of the days preceding the field measurements. Some critical observations on the statistical analysis of chlorophyll a fluorescence parameters are also made.

Caloplaca badioreagens is a new endolithic species of subgenus Pyrenodesmia characterized by a greyish brown, K+ reddish brown epithecium, and simple, non-capitate paraphyses. It is readily distinguishable from other endolithic Pyrenodesmias (C. agardhiana, C. alociza, C. erodens) by the presence of an unknown lichen substance in the excipulum and the subhymenium, forming large, rectangular crystal plates in GAW and GE. The new species was collected on hard limestone in three localities of central and southern Italy.

The development of isidia in thalli of Pseudevernia furfuracea from the Carnic Alps (North-eastern Italy), and the effects of these structures on CO2 gas exchanges were investigated. The ontogenetic events were studied by comparison of sections stained with different histochemical tests and SEM observations. A high cell turnover rate in both symbiotic partners is the first sign of isidium development, followed by an increased aplanosporogenesis of algae and growth of neighbouring medullary hyphae which become oriented upwards. Large nuclei and an intense cytoplasm activity characterize the mycobiont cells. The surface of very young isidia shows an irregular structure of spherical to ovoid protruding tips of perpendicular cortical hyphae, that are later organised in a pseudomeristematic area similar to that observed in the apex of growing lobes. CO2 gas exchange measurements carried out in the laboratory confirmed the high metabolic activity of isidia. At optimal water content and favourable light conditions, isolated isidia had rates of gross photosynthesis and dark respiration that were twice those of non-isidiate lobes. Isolated isidia also had a very low CO2 saturation point, probably because of their favourable surface/volume ratio, and a high light saturation, probably linked to their high content of photosynthetic pigments. The different roles played by isidia in the biology of Pseudevernia furfuracea, and particularly their rejuvenating effect on aged lobes, are discussed, and the presence of thalloconidia is briefly mentioned.

The factors influencing the predominance of one of the two mineral forms of calcium oxalate (CO), the monohydrated whewellite (COM) and the di-hydrated weddellite (COD), forming the pruina of the upper cortex of lichens, have been investigated through a simple, sensitive histochemical assay: toluidine blue O (TBO), a metachromatic staining test. The differential reactivity of 43 thalli of 17 pruinose foliose species, supplemented by X-ray diffraction analysis and observations with polarizing and scanning electron microscopy, suggests that the histochemical reactivity of hyphal walls and cementing substances of the upper cortex are related to the density of anionic charges. These factors are probably due to the occurrence of polyuronic acid substances that strongly affects the mineralization of CO. Di-hydrated wedellite is always associated with TBO metachromatic reactivity, and COM with orthochromatic reactivity. When the material has an ambiguous ortho/metachromatic reactivity, COD and COM may occur together. This study presents the first experimental evidence that in lichens CO biomineralization is at least partially biologically controlled.

A survey aimed at studying the effects of hydrogen sulphide (H2S) on epiphytic lichen vegetation was carried out at Acquapassante (Mt. Amiata, Central Italy). In 1992, lichen vegetation was surveyed using a sampling grid often units, on 18 chestnut trees along a transect from a chimney emitting H2S to c. 200 m in the direction of the prevailing winds. A Lichen Biodiversity Index (LBI) was calculated as the sum of the frequencies of all species present within the grid. The same survey was repeated five years later. Concentration Analysis was applied to describe the data structure, and Procrustes Analysis was used to verify the congruence between the ordinations of 1992 and 1997. The statistically significant linear and non-linear regressions found between environmental variables (distance of relevés from the chimney, bark pH, lichen biomass of selected foliose and fruticose species, total sulphur content of Evernia prunastri, Hypogymnia physodes, Parmelia sulcata and Ramalina fastigiata) and the position of the relevé points on the ordination axes suggest that species distribution along the transect is related to differences in H2S tolerance. However, some crustose species (Lecanora cf. conizaeoides, L. saligna and Scolkiosporum umbrinum) should be probably excluded from the computation of the LBI for monitoring purposes, as their optimum is in the immediate vicinity of the H2S source.

Lecania pusilla Tretiach sp. nov. is described from the Trieste Karst, where it was collected twice on epilithic mosses in protected overhangs. The new species is characterized by simple or uniseptate spores, pruinose apothecia, and Bacidia-type asci; it has a reduced, granular thallus with no lichen substances.