Introduction

The information derives from the latest checklist of the lichens of Italy by Nimis (2016), that summarises 23 years of lichenological research in Italy, starting from the first annotated catalogue by Nimis (1993). In this period, a new generation of Italian lichenologists grew up, and several non-Italian lichenologists published many new records from Italy: more than 1200 papers appeared after 1993, which contain at least one lichen record from the country. An updated, non-annotated list of accepted taxa was published by Nimis & Martellos (2003), followed by a further nomenclatural updating available online since the end of 2007 in ITALIC, the Information System on Italian Lichens (see Nimis & Martellos 2002).
In order to facilitate comparisons with the first checklist (Nimis 1993), also that by Nimis (2016) includes: a) all of the lichenised taxa known from Italy, b) non-lichenised taxa belonging to genera with lichenised representatives, c) a selection of non-lichenised fungi which were traditionally treated by lichenologists. A complete checklist of lichenicolous fungi is in preparation by W. von Brackel, and a preliminary list, including 492 infrageneric taxa, was published by Brackel (2016).
The checklist by Nimis (2016) includes 2704 accepted infrageneric taxa, 2565 of which are lichenised. The increase in the number of taxa from 1993 to 2016 is summarised in Tab. 1.


Tab. 1 - Progress in the lichenological exploration of Italy from 1993 to 2016.

The increase is obviously highest in the previously least explored regions, but on the whole it is consistent throughout the country, which is presently much more homogeneously studied than in 1993. On the contrary, the study of different lichen biota within Italy was much less homogeneous. Epiphytic lichens were studied more intensively than those growing on other substrata, mainly because of the very high number of biomonitoring studies carried out in Italy in the last decades, first in disturbed environments, and more recently in forests. Saxicolous and terricolous lichens were studied much less, with the exception of saxicolous species on monuments. Among the areas which are still poorly investigated, the following may be cited: 1) The central Apennines, especially the siliceous Monti della Laga and the mountains of Lazio in central Italy, 2) the northern Apennines in the Emilia-Romagna and Marche regions, 3) the coastal mountains of Campania, 4) the low-elevation deep valleys along the Adriatic side of the Peninsula, 5) the calcareous canyons of Puglia called gravine, 6) the gypsum outcrops of Sicilia, 7) the Astragalus-formations of the high Mediterranean mountains (Calabria, Sicilia and Sardegna, see Nimis 1981). Despite the relatively high number of known species, the Italian Alps as well are worthy of a more intense lichenological exploration.
Most of the records accepted by Nimis (2016) derive from published sources. It is obvious that not all of them could be accepted uncritically: the circumscription of taxa may differ among authors, recent taxonomic revisions might have demonstrated that a given taxon actually includes several taxa of the corresponding rank, some authors may be more reliable than others, etc. The author of a checklist is often forced to make difficult decisions, since in most cases it is not possible to check directly all identifications cited in the literature. Identifications in the Iberian literature were checked by Giralt (1997) for two genera: Ochrolechia and Rinodina: the number of misidentifications, even by "trustworthy" authors, proved to be very high. In the checklist by Nimis (2016), a pragmatic approach was taken: the list of records is the result of a series of "educated guesses" for which the author took full responsibility. Not all of the published records were accepted: particularly dubious ones are mentioned in the notes, but are not attributed to the respective regions. Eventually, however, it will be up to the reader to judge the reliability of literature data.
The selection of sources is a delicate task as well: should only properly published records be accepted, or should unpublished sources and "grey literature", such as theses, private reports, excursion guides, herbaria etc., also be taken into consideration? In the checklist by Nimis (2016), the only cogent criterion was that the material on which the records are based must be retrievable. Unpublished theses may often contain extremely valuable information, provided that vouchers are deposited in the herbarium of the institution at which the thesis was carried out. If such information is considered as important and valid, it is included in the checklist. Records deriving from non-published Herbarium specimens were included only when they are new to Italy and/or to an administrative region, and when their metadata, especially concerning the locality, are available online (e.g. those from B, M, UPS, TSB, Herb. Vondrák, etc.). In a very few cases Nimis (2016) has included records deriving from personal observations, when it was not possible to collect the material: typical is the case of Acarospora moenium observed on the private wall of a house near Trieste, which, for obvious reasons, could not be collected.
One could wonder whether it has a sense to cite every single report of widespread and common species, such as Lecidella elaeochroma or Xanthoria parietina, which are certainly occurring throughout the country. The reason is that the number of literature records is in itself an important datum, which was used to estimate the commonness/rarity of each species in different biogeographic subdivisions of the country (see later).
For obvious reasons of space, in the notes to genera and species Nimis (2016) tried, as far as possible, to avoid repeating literature citations already reported in the first annotated checklist (Nimis 1993). The comments to species should be considered as a complement, rather than a substitution, of those published in the previous checklist.
Checklists are also expected to be a reference for nomenclatural matters, at least for some years. In this respect, however, the checklist by Nimis (2016) will likely fail. After the nomenclatural updating by Nimis & Martellos (2003) many names have already changed, and many are likely to change in the future. This is mainly due to two facts: 1) The explosion of molecular phylogeny, which is bringing about a true revolution in the taxonomy of lichenised fungi, 2) The unfortunate fact that in the current binomial system the genus rank, contrary to all other supraspecific ranks, is an integral part of the names we give to organisms (Nimis 2001, 2005). Names, which should intrinsically remain stable, are thus changing continuously, depending on the ever-changing hypotheses on phylogenetic affinities. Nimis (2016) tried to follow the most recent taxonomic proposals, including several which he accepted with hesitation, like those concerning the Teloschistaceae and the difficult genus Aspicilia: molecular data are lacking for many species, and these still have to stay in the old "container genera" such as Caloplaca s.lat. and Aspicilia s.lat. The molecular revision of species and higher taxa is far from being completed: many cryptic species are being described, and many genera will undergo further splitting in the next future.
In any case, checklists may be valuable tools for retrieving and accessing the enormous amount of information which has accumulated during centuries of biological research. They offer an indispensable basis for specimen revision, for the critical reappraisal of poorly-known taxa, and for the further exploration of under-investigated areas. In this sense, checklists may and should be catalysts for new, more intensive investigations. The best criterion for a checklist to have accomplished its task as a facility to the scientific community is the speed of its becoming outdated, which is what we paradoxically wish for the present database.