Pier Luigi Nimis

Towards a checklist of Mediterranean lichens

Abstract

Nimis, P.L.: Towards a checklist of Mediterranean lichens. - Bocconea 6:
 5 - 17. 1996 - ISSN 1120-4060.
The OPTIMA Commission For Lichens is supporting an international project for
 a compilation of a general checklist of lichens of the Mediterranean
 region. This paper describes the history of the project and the present
 State of the Art, with some critical considerations about the delimitation
 of the Mediterranean area for a lichen checklist, and a short outline of
 the main phytogeographic features of southern Europe, as far as lichens are
 concerned. It is suggested that the national checklist produced in the
 framework of the project should become available on the Internet, with a
 possibility of continuous updating by the international lichenological
 community.

        In the last years, mainly as a consequence of the UNESCO Conference of Rio
 and of the associated increase in research funding, biodiversity has become
 a focal issue in environmental research, its estimate being recognized as
 essential for managing ecosystems on a global scale. As it often happens
 when a scientific term becomes popular and vulgarized, the term
 "biodiversity" - which, incidentally, was already difficult to define
 within his original context - is often used in a rather vague sense,
 without a strict operational definition. The most widespread acception is
 to consider it as equivalent to the number of taxa occurring in a given
 Operational Geographic Unit (OGU, see Crovello 1981), i.e. a site, a
 particular area, a country, a continent... Such a definition, however, is
 far from being satisfactory. Once it is known that in a given OGU there is
 a given number of certain organisms, the question arises: is the
 biodiversity of this OGU high or low ? Thus, the quantification of
 "biodiversity" implies a quantitative comparison with areas of more or less
 equal size and similar ecological conditions. This is a controversial and
 interesting field, in which much more research and basic data are needed.
 The relations between number of species, latitude, area size, ecological
 complexity, etc. have been the object of study since the beginnings of this
 century (Arrhenius 1921, Gleason 1922); the problem, however, being
 exceedingly complex, is far from being fully resolved (see e.g. Preston
 1962, Johnson & Raven 1970, Malyshev & al. 1994). The difficulties are
 exacerbated by the widespread lack of accurate and comprehensive data on
 the number of organisms occurring in OGUs of different surface.

        In botany and mycology, comparative biodiversity estimates are usually
 based on national, regional or local floras, which are more or less
 accurate inventories of the organisms occurring in a given area. The
 quality of the available information, however, differs strongly among
 taxonomic groups. Vascular plants were studied more thoroughly, while for
 other groups of organisms basic information is often scanty, and sound
 biodiversity estimates are practically impossible. This is the case of
 lichenized and lichenicolous fungi in most of the world, including southern
 Europe, even though Europe is certainly the lichenologically best known
 part of the world. Spain, France and Italy, in particular, have witnessed a
 dramatic increase in the intensity of lichenological exploration in the
 last 20 years. Nevertheless, the knowledge of the south European and
 Mediterranean lichen floras was and still is largely insufficient. There is
 a huge number of papers dealing with lichens of this region, but no effort
 towards a general synthesis was ever attempted, several taxa still await
 critical revision, and large areas remain virtually unexplored by
 lichenologists. Considering this state of affairs, any attempt towards a
 general assessment of lichen biodiversity in the Mediterranean region is
 premature. The reader can easily imagine what is the situation in other
 parts of the world, and for many other groups of organisms. Real advances
 in biodiversity research can be only achieved by intensified work along
 three lines: a) syntheses of the hitherto available data, b) taxonomic
 research, c) exploration of poorly known areas.
        The present volume of Bocconea, published under the auspices of the OPTIMA
 Commission for Lichens, is the second contribution, after the checklist of
 the lichens of Italy (Nimis 1993), towards a synthesis of available data on
 lichen biodiversity in the Mediterranean region and southern Europe. It
 presents checklists of lichens (some including lichenicolous fungi) for
 four extra European, Mediterranean  countries: Morocco, Tunisia, Israel,
 Mediterranean Turkey, and for a south European country that has many
 lichens in common with the Mediterranean, the Ukraine. Further checklists
 will be issued in the next future. The principal aim of these publications
 is to provide a solid starting point for further taxonomic and floristic
 research, and a foundation for a better our understanding of the south
 European and Mediterranean lichen flora.

Activity within OPTIMA: 1989-1993

        The checklists published in this volume are the product of an international
 project by the OPTIMA Commission for Lichens, aiming at the compilation of
 an inventory of biodiversity of lichens and lichenicolous fungi in the
 Mediterranean area. The idea of producing a checklist of Mediterranean
 lichens was first put forward by Josef Poelt during a lichenological
 excursion to Sardinia in 1986. Two years later I was asked to organize a
 lichen session in the framework of the VI OPTIMA symposium, held in Delphi
 (Greece) in September 1989. The session was entirely devoted to floristic
 and phytogeographical problems concerning Mediterranean lichens, and all
 invited speakers, while trying to present the best possible syntheses in
 their respective fields, underlined the extreme need for further synthetic
 work, and for ongoing taxonomic and floristic research (Barreno 1991, Egea
 & Llimona 1991, Roux 1991, Scheidegger 1991). On that occasion, Poelt's
 idea was first presented in public, and discussed by a large group of
 lichenologists. It was then decided to create a Commission for Lichens
 within OPTIMA, with the main task of promoting and coordinating efforts
 toward the compilation of a checklist. Members of the Commission were E.
 Barreno (Valencia), J.M. Egea (Murcia), X. Llimona (Barcelona), H.
 Mayrhofer (Graz), D. Ottonello (Palermo), J. Poelt (Graz), C. Roux
 (Marseille), C. Scheidegger (Bern), and I myself acting as the secretary.
 Thanks to funds obtained from the University of Trieste, the Commission
 held its first official meeting there on 20-21 April 1990. The participants
 agreed on a practical approach to the lichen Med-Checklist, an open process
 involving several stages with increasing levels of sophistication. The
 original idea was to prepare, in a relatively short time, a "first
 approximation checklist", to be followed by a series of updated, more
 complete versions. This checklist was supposed to contain a complete list
 of taxa with relevant synonymy, notes on ecology and distribution, and
 references to relevantliterature. Critical, or imperfectly known taxa
 were to be included, with their special status flagged. The checklist was
 to reflect the present state of knowledge, which of course was uneven for
 the various taxonomic groups and geographical subdivisions, to pinpoint
 open problems, and to highlight areas in which further research was most
 urgently needed.
        At that time most of the participants agreed that the "first approximation
 checklist" was to be limited to southern Europe, excluding Africa and Asia,
 the reason being that lichenological knowledge of most non-European areas
 was exceedingly poor. The subdivision of the checklist area was to be based
 on practical criteria, such as the degree of lichenological knowledge, and
 the presence of active lichenologists in each area. The following
 subdivisions were then agreed upon: Portugal (Lu), Spain (Hs), Baleares
 (Bl), Southern France (Ga), Corsica (Co), Peninsular Italy (It), Sicily
 (Si), Sardinia (Sa), Yugoslavia (Yu), Albania (Al), Greece (Gr, including
 the eastern islands - AE), Crete (Cr, including the Karpathos group), and
 European Turkey (Tu). The participants to the Trieste meeting saw no point
 in limiting the check-list to areas with truly Mediterranean vegetation,
 considering that many lichens have very broad distributional ranges, and
 that the lichens of sub-Mediterranean regions are also poorly known in a
 general way. The Alps were deliberately excluded for practical reasons: a
 lichen checklist for the Alps would by itself have been worthy of an
 independent project.
        In Trieste a provisional list of Regional Advisers was drawn up. Their role
 was to check all informations relative to their region, propose additions
 or emendations, and contact, if necessary, other lichenologists from the
 same area. A second provisional list was prepared, including specialists of
 various taxonomic groups: they were to provide, for the groups in which
 they were specialized, a preliminary list of all species known to occur
 within the checklist area. Many proposed advisers and specialists were
 contacted by members of the Commission during the International Mycological
 Congress held in Regensburg (Germany) in August 1990, and most agreed to
 collaborate in the project.
        Back from Regensburg, in September 1990, I began to work on a provisional
 list for Italy (including Sardinia and Sicily). The amount of taxonomic and
 floristic problems that arose in the very first stages of this process was
 so huge, that the prospects of rapidly producing an albeit "first
 approximation" checklist for all of southern Europe came to appear as
 utterly unrealistic. I had to cope with a literature which, at the end,
 summed up to more than 1.500 titles, with a plethora of forgotten names,
 and with taxonomic groups whose intricated taxonomy was far from being
 solved. Furthermore, different authors had - as usual - different species
 concepts, some authors were - of course - more reliable than others, and I
 was forced to make many delicate choices in accepting or rejecting given
 records. Finally, many problems could be solved only by the direct
 examination of herbarium specimens, and the old Italian herbaria were full
 of invaluable material which, since one century, patiently awaited
 revision. The compilation of a kind of "first approximation checklist" for
 Italy alone took me two full years of hard work, and resulted in a bulky
 volume of 897 pages (Nimis, 1993). This trial run, however, was useful to
 test the system of specialists and regional advisers, which proved to work
 very well.
 

Activity within OPTIMA: after 1993

        Steady contacts with members of the OPTIMA Commission for Lichens during
 the compilation of the checklist of Italy, brought about a radical change
 of the original project framework. The main modifications, informally
 agreed among the Commission members, were as follows:
  The general checklist would be preceeded by regional lists, summarizing in
 a critical form the information available for the different regions.

  The authors of the regional checklists would be free to adopt, for the
 time being, the nomenclature and species concept they like best. Attempts
 towards uniformization would have to await a later stage, when more
 national checklists would be available.
        The reasons for these decisions will be discussed in the next two chapters.
 

        During the VIII OPTIMA Meeting, held in Sevilla in September 1995, another
 Lichen Symposium was organized, which was fully devoted to the presentation
 of some new checklist that are published in the present volume of Bocconea.
 On that occasion, a new Commission for Lichens was appointed for the period
 1995-2001. The new Commission is composed by the following members: P.L.
 Nimis (Trieste, secretary), E. Barreno (Valencia), A. Crespo (Madrid), J.
 M. Egea (Murcia), M. Galun (Tel-Aviv), V. John (Bad Durkheim), X. Llimona
 (Barcelona), H. Mayrhofer (Graz), D. Ottonello (Palermo), C Roux
 (Marseille) and M. R. D. Seaward (Bradford).
        The first five checklists compiled according to general considerations
 discussed above are presented in this volume. The state of the art of the
 Med-checklist project in 1996 is the following:

        Albania. - This is one of the least-known parts of Mediterranean Europe.
 The University of Trieste has financed a project aiming at the production,
 after a period of field-work in 1997, of a checklist for Albania by the end
 of 1998, produced by J. Hafellner (Graz) and M. Tretiach (Trieste).
        Algeria. - Work is in progress by several authors in Algeria, France and
 Spain to produce a checklist of lichens of Algeria by the end of 1997,
 which will also include the revision of many of the taxa described by
 Werner.
        Italy. - The checklist of Italian lichens was the first to be published
 (Nimis 1993). It included 2,145 infrageneric taxa, with a geographical
 breakdown into 20 different administrative regions, including Sicily and
 Sardinia. An abridged version, without the critical notes on the taxa and
 with the references limited to post-1993 papers, is being continuously
 updated, and will be available on the Internet, probably by the end of
 1996. By May 1996 the number of accepted infrageneric taxa (excluding most
 lichenicolous fungi) has risen to 2,200. A catalogue of the lichenicolous
 fungi of Italy, by Triebel and Nimis, is in preparation, and will probably
 be published in the first half of 1997.
        Iberian Peninsula (Spain and Portugal). - The Spanish Lichen Society has,
 with the main aim of producing a lichen flora of Spain and Portugal,
 elaborated a checklist in the form of a guide to the bibliographical
 sources of published floristic information. The data are stored in a FoxPro
 database, designed by N.L. Hladun (Barcelona). Each entry (usually a
 species name) is followed by the citation, in chronological order, of the
 sources (authors, date of publication, page and number of references). Up
 to now, data from 1,466 sources have been incorporated (170 with data from
 Portugal only, 824 limited to Spain). Altogether, 41,576 data were entered,
 usually corresponding to 1-10 records each. A more detailed list for
 Portugal is planned for the next future by Palmira Carvalho (University of
 Lisboa). The checklist for the Iberian Peninsula will be ready by the end
 of 1996. The number of hitherto accepted infrageneric taxa is about 1,900
 (Llimona, pers. comm.).
        Israel. - A checklist is published in this volume by Galun & Mukhtar. It
 contains a list of references, and includes unpublished records of the
 lichens hitherto known from Israel. The total number of infrageneric taxa
 is 234.
        Morocco. - The checklist of lichens and lichenicolous fungi of Morocco is
 also published in this volume by Egea. It is based on literature data, and
 on the results of original investigations of that area. For each taxon, the
 following informations are included: accepted name, most relevant synonyms,
 and bibliographical references, given separately for 9 geographical
 subdivisions of the country. The checklist includes 1,100 infrageneric
 taxa, 1,058 of lichenized, 42 of lichenicolous fungi.
        Tunisia. - This checklist too is published in this volume, by Mark
 Seaward. A previous inventory of the Tunisian lichen flora, dating back to
 the 1950s, recorded 186 species from fragmentary and widely scattered
 published sources. The new, detailed literature survey, supplemented by
 herbarium studies, and the collections made by the author in 1973, has
 shown the currently known Tunisian lichen flora to comprise 415
 infrageneric taxa.
        Turkey. - The checkist published in this volume by V. John is limited to
 the Mediterranean part of Turkey, and covers both lichenized and
 lichenicolous fungi. This area covers nine provinces directly adjoining the
 Mediterranean sea, and two bordering provinces. The checklist is based on
 literature records, herbarium specimens, and original field work. The total
 number of accepted infrageneric taxa is 459.
        Southern France - The author responsible for the checklist of the lichens
 of southern France is Claude Roux (Marseille), the co-author of one of the
 most important identification books for European lichens that appeared in
 this century (Clauzade & Roux 1985). Both authors provided further
 fundamental contributions to the knowledge of the Mediterranean lichen
 flora, also published a comprehensive key to lichenicolous fungi worldwide
 (Clauzade & Roux 1989). Both works are presently being updated, which may
 somehow justify the slow progress in the compilation of a checklist for
 southern France, originally planned as one of the first to be issued within
 the project. That checklist, however, is of fundamental importance for the
 project, since southern France is one of the best-known parts of the
 Mediterranean region. It will be probably available in c. one year.
        Slovenia. - A checklist Slovenian lichens is being compiled by H.
 Mayrhofer and collaborators (Graz), jointly with A. Batic (Ljubljiana). It
 will be based on literature records and on a conspicuous body of original
 collections made in different parts of the country, and will be ready
 before the end of 1996.
        Ukraine - Although this is definitely a non-Mediterranean country, the
 Ukraine includes a large portion of the Black Sea coast, and notably the
 Crimea, with its quasi-Mediterranean climate. For this reason, the
 checklist of Ukrainian lichens is relevant for the project. This checklist
 is published in this volume by Kondratyuk and co-workers, and includes
 reference to 1,259 infrageneric taxa.
        Macaronesia. - A checklist of the lichens and lichenicolous fungi of
 Macaronesia (Canary Islands, Madeira and Azores) has been published by
 Hafellner (1995). It will be continuously updated by the author within the
 framework of the OPTIMA project.
 

        Other countries. - For the following countries no new checklist is in
 sight, although older checklists, or more or less complete bibliographical
 lists sometimes exist that could serve as a basis for an updated inventory:
 Bulgaria, Croatia (an old checklist available: Kusan 1953), Cyprus
 (contacts with potential authors already taken), Egypt, Greece, including
 Crete (a modern literature survey available: Christensen 1989, contacts
 with potential authors are in progress), Lebanon, Lybia, F.Y.R. Makedonija
 (an old checklist available: Kusan 1953), Malta, Romania, Yugoslavia
 (Serbia and Montenegro: an old checklist available: Kusan 1953).
 

Delimitation of the "Mediterranean Region"

        In planning a checklist of "Mediterranean" lichens we had to face the
 question of defining the term "Mediterranean", and delimiting the
 corresponding geographic area. For this purpose, different criteria -
 climatic, vegetational, biogeographic - can be used, jointly or
 individually, resulting in various, sometimes widely different
 delimitations (see e.g. Margaris & Mooney 1981, Kruger & al. 1983, Quézel
 1985, Rivas-Martinez 1987). A widespread view considers as truly
 "Mediterranean" all areas with an evergreen sclerophyllous vegetation
 dominated by Quercus ilex, or, in the eastern Mediterranean region, by Q.
 calliprinos (see, however, the objections by Emberger 1943); the so-called
 Oleo-Ceratonion vegetation is included as a marker of the warmest an driest
 Mediterranean climate conditions. A different criterion for "Mediterranean"
 climatic conditions is the present, cultivated distribution of the Olive
 tree (Olea sativa). Several climatic indexes were also proposed to define
 the "Mediterraneity" of a given area (e.g. by Daget 1977a-b, Tukhanen 1980,
 Box 1982). However, the regions bordering the Mediterranean Sea have such
 wide temperatures and rainfall ranges (from 100 mm in pre-desert zones to
 more than 3000 mm on some mountains), as to render any kind of quantitative
 climatic definition very problematic (Quézel 1985). All such definitions
 are of scant interest for our planned lichen checklists. One of their
 common, drawbacks is that it is extremely difficult, in practice, to
 delimit truly "Mediterranean" OGUs due to the complicated geomorphological
 and orographical situation of the countries surrounding the Mediterranean
 Basin. Even if all authors were to agree on an uniform set of criteria for
 classifying an OGU as "Mediterranean", the evaluation of literature records
 would be far from easy: for every locality one would have to check whether
 or not it falls within a "Mediterranean" OGU, when the required information
 is likely missing in most of the relevant literature.
        Apart from the difficulties of geographic delimitation, there are other
 good reasons for adopting a broad concept of the term "Mediterranean" for a
 lichen checklist. One such reason is that lichens, as most cryptogams, have
 far broader distributional ranges, on average, than higher plants.
 Phytogeographical subdivisions based on lichen data differ from those based
 on the distribution of higher plants. Lichens, being excellent indicators
 of climatic parameters such as temperature and air humidity, can provide
 valuable information on the phytoclimatic characteristics of a region.
 Also, as will be discussed in the next chapter, the number of lichens with
 truly "Mediterranean" range is extremely small when compared to that of
 animals or vascular plants. Lichen checklists covering a broad area will be
 much more informative, with respect to distribution patterns of  taxa, than
 those limited to narrow areas. Another reason has to do with the
 biogeographic peculiarities of southern Europe. The highest peaks of the
 Mediterranean mountains do neither have a truly Mediterranean climate, nor
 do they host a sclerophyllous vegetation. However, they are
 biogeographically so peculiar that the existence of an "Oromediterranean"
 vegetation belt is accepted by most authors, albeit under different
 denominations. Similar considerations apply to intermediate vegetation
 belts, such as the Cedrus forests of the mountains of Mediterranean Asia
 and North Africa. They  show little affinity to evergreen sclerophyllous
 vegetation, yet they are a typical, unique feature of the Mediterranean
 region in the wide sense. The floristic, phytogeographical and historical
 affinities of the Macaronesian flora with that of the Mediterranean proper
 are so obvious that Macaronesia must not be ignored in a comprehensive
 treatment of Mediterranean biodiversity. Finally, in the northern part of
 the Mediterranean region deciduous forest form a belt just above the
 sclerophyllous vegetation, and the two biota often intermingle. Italy is a
 good example, where
deciduous oaks are much more frequent, sometimes even
 at low elevations, than evergreen vegetation, and where beech (Fagus
 sylvatica) forms the tree-line from the northern Apennines down to the
 mountains of Sicily. Deciduous woods, and especially beech forests, are
 admittedly not the most characteristic examples of "Mediterranean"
 vegetation. Yet, southern Europe was the principal refugial area, during
 the glacial period, for the temperate nemoral flora of Europe (Nimis &
 Bolognini 1993, Bolognini & Nimis 1993). What may now appear to be a
 typical example of "Central European" vegetation, such as a German beech
 forest, is in reality a very much impoverished version of a type of biome
 that has its roots, and maintains its maximum diversity in the mountains of
 the Mediterranean region. This holds true for vascular plants and for
 lichens alike. Many species of the deciduous forest belt - "Central
 European" or "submediterranean" species, as they are often called -
 colonized Central and northern Europe from the south. To my mind, one of
 the prime reasons not to limit our lichen checklists to "truly
 Mediterranean" areas is, that information on the distribution of lichens
 throughout southern Europe and in different altitudinal belts of the
 Mediterranean is paramount for understanding the post-glacial
 re-colonization of more northern areas.

Phytogeographical patterns in the "Mediterranean" lichen flora

        In the lichenological literature the term "Mediterranean" has often been
 used exactly as for vascular plants. Many authors (e.g. Nimis & Poelt 1987)
 implicitly assumed the existence of a "Mediterranean element" in lichens,
 whose distribution patterns would be consistent with those of steno- or
 eurimediterranean vascular plants. Barreno (1991) was one of the first to
 question this assumption, suggesting that examples of truly "Mediterranean"
 distribution are far less frequent in lichens than in vascular plants. She
 pointed out that many terricolous "Mediterranean" lichens are distributed
 far beyond the Mediterranean region, some of them extending throughout the
 Mediterranean, Irano-Turanian and Saharo-Arabian floristic provinces, a
 range that corresponds well with the Isoclimatic Mediterranean Area
 proposed by Daget (1977a,b), and with the "Mesogean Subempire" of Quezel
 (1978). The puzzling paucity, among lichens, of cases of truly
 "Mediterranean" distribution patterns was confirmed by the phytoclimatic
 analysis of the Italian lichen flora of Nimis (1993) and Nimis & Tretiach
 (1995). To date, Italy is the only country of southern Europe for which it
 is possible to attempt an albeit preliminary phytogegraphic synthesis for
 lichens. The lichen flora of Italy is composed by three main elements:

- A mainly temperate element linked to the deciduous forest belt, without
 particular suboceanic affinities (38% of the total flora), which is well
 represented in all regions, but scarcely penetrates eu-Mediterranean
 vegetation (e.g. several species of Parmelia and Phaeophyscia, or otherwise
 common temperate lichens such as Candelaria concolor or Candelariella
 reflexa are quite rare in the southern Mediterranean region, where they are
 mostly confined to the "submediterranean" vegetation belt).

- A suboceanic to oceanic element with more or less evident subtropical to
 tropical affinities, confined to humid climates which, in Italy, is most
 frequent along the western side of the Peninsula, in Liguria and in
 Sardegna (c. 20% of the total flora); this element is more important in
 western Europe, while in southern Europe and the Mediterranean region it is
 tied to areas with suboceanic climatic conditions (humid mountains,
 Tyrrhenian and Dalmatian coasts, Colchis, etc.).

- A northern element, restricted to the highest mountains, most frequent
 in the Alps and becoming progressively rarer southwards (c. 25%); in the
 Mediterranean region this element, which in northern and central Europe is
 generally bound to the arctic-alpine or boreal-oroboreal vegetation belts
 and which includes many species with a northern, holarctic distribution,
 reaches far more southern latitudes than the corresponding element in
 vascular plants, especially on siliceous substrata. Many "northern" species
 are still present on e.g. Tenerife, in the Atlas Mountains, and the
 siliceous mountains of Turkey. On the whole, there is a sharp
 phytogeographical difference between siliceous and calcareous substrata in
 Europe: the northern element tends to prevail on the former, whereas on
 calcareous rocks there is a higher incidence of "southern" species (Nimis &
 Tretiach 1995). A satisfactory interpretation of this fact will require
 further, intensive taxonomic research, and a much better knowledge of the
 lichen flora of the Himalayas, supposedly one of the main areas of origin
 and differentiation of the "southern" calcicolous flora.
        The remaining 16% of the Italian lichen flora can be distributed among
 three smaller elements, each with peculiar distribution:

- South European orophytes (7%) a group including several poorly-known,
 "endemic" taxa.

- Widespread xerophytic species (2%), an element including the "Mesogean"
 element of Barreno (1991), which in Italy is scarcely represented due to
 the rarity of truly arid types of climate, but that has a stronger presence
 in N Africa, SW Asia and parts of the Iberian Peninsula.

-  "Mediterranean" species (8%), an element whose incidence is quite low,
 when compared to the proportion of Mediterranean vascular plant species in
 the Italian vascular flora. For example, steno- plus eurimediterranean
 species account for 28.5% of the vascular flora of Sicily (Nimis 1984),
 whereas the corresponding figure for lichens is only 8.9 % (Nimis &
 Tretiach 1995). The "Mediterranean" lichen element is difficult to define
 and quite heterogeneous, as it includes: (a) several, often not very
 well-known, coastal species restricted to the Mediterranean region, (b)
 those species with a Macaronesian-Mediterranean distribution not bound to a
 particularly humid climate, (c) a few species extending into other parts of
 the world with a Mediterranean climate, especially California, (d) some
 species restricted to the humid belt of the Mediterranean mountains.
 Perhaps the richest habitat for truly "Mediterranean" lichens are humid
 rock outcrops, both siliceous and calcareous, along the coasts, which host
 a very peculiar and often geographically differentiated flora (see e.g.
 Roux 1991). The epiphytic vegetation, on the contrary, is much more
 homogeneous throughout the Mediterranean region. According to Nimis (1993)
 the scarcity of truly "Mediterranean" lichens might be explained by two
 main reasons: (a) a summer drought period does not result in a sufficient
 strong selective pressure for the evolution of a truly Mediterranean lichen
 flora, many lichens being anyhow able to withstand long periods of drought,
 (b) the evolution of a Mediterranean-type climate in southern Europe is too
 recent to permit the differentiation of a specialized flora in a group of
 organisms such as lichens which, supposedly, have a very low rate of
 evolution.

        Summing up, the lichen flora of the Mediterranean region appears to be
 mainly constituted of four broadly defined phytoclimatic elements: a
 northern element, a temperate element, a humid subtropical element, and an
 arid subtropical element. The "Mediterranean" or
 "Mediterranean-Macaronesian" element, while an interesting, probably very
 old relic of Tertiary times, is not, at least in sheer number, the most
 peculiar feature of the Mediterranean lichen flora. Its relationships with
 the humid subtropical and the arid subtropical floras still await full
 elucidation, both at the taxonomic and biological-ecological level. A
 characteristic feature shared by "Mediterranean" and arid subtropical
 lichens is the high frequency in these phytogeographic groups of parasitic,
 or parasymbiotic species (Poelt & Doppelbaur 1956), perhaps linked to the
 scarcity of free-living photobionts in arid areas. In my opinion, and
 contrary to the prevailing view, another biologically and
 phytogeographically very interesting element is the temperate one. All
 other elements - with the exception, of course, of the few typically
 Mediterranean lichens - have their main center of origin outside the
 Mediterranean region, whereas many temperate species have once migrated
 towards the north (and east) from areas bordering the Mediterranean Sea.
 This migration has left several traces in the lichen flora of the southern
 areas, and many more probably await discovery. One peculiarity of the
 Mediterranean flora was highlighted by Poelt (1970) in his classic Theorie
 der Artenpaare: he demonstrated that in the European flora there are
 several cases of species closely related pair-wise, one reproducing
 sexually, the other asexually. The members of these "species pairs" often
 have different distributions, the "primary", sexually reproducing species
 being more frequent at southern latitudes, the "secondary", asexual species
 tending to be more widespread, and hence more northerly. This tendency is
 most probably related to the post-glacial colonization of central and
 northern Europe by populations coming from the south. Another, related
 feature of the Mediterranean lichen flora is the noth-to-south increase of
 genetic diversity found in several groups of of temperate lichens.
 According to Leuckert & Poelt (1978) chemically heterogeneous groups tend
 to be distributed along a north-to-south gradient: in the south there are
 more numerous and more complex chemotypes. This situation is found in
 widely different families and genera, at least among saxicolous, sexually
 reproducing species, and is interpreted as a result of recent
 impoverishment in northern regions, due to the effects of glaciation. The
 higher genetic diversity of the southern flora is also evident at the
 morphological level. A typical example is Lecanora muralis, one of the most
 common saxicolous species of Europe, extending to the Arctic, and well into
 large urban agglomerations of Central Europe. The species is very variable,
 and several morphs have been distinguished (Seaward 1976); in the north,
 however, most of the variability is environmentally induced. In the
 Mediterranean area, on the contrary, Lecanora muralis consists of many
 morphologically, ecologically and probably also chemically different taxa,
 that still await thorough taxonomic revision. Examples of this kind are
 numerous, and often concern very widespread and common temperate lichens
 such as  Lecidea fuscoatra, the Lecanora dispersa complex, the Lecanora
 rupicola complex, etc. The lichen flora of the countries bordering the
 Mediterranean sea appears as a kind of reservoir of genetic diversity for
 the development of the temperate lichen flora, from which only a few
 representatives managed to migrate northwards in post-glacial times. These
 considerations suggest that it would be very short-sighted to focus our
 attention only on truly "Mediterranean" lichen floras.

Some considerations about the checklists

        Checklists, generally, summarize in a more or less critical way the
 hitherto known information on the biodiversity of a given group of
 organisms in a given area. They may differ greatly in scope and content: in
 some cases they appear as simple lists of names, in others they provide
 detailed literature records for all listed taxa. All checklists presented
 in this volume are based on properly cited literature records, thus
 providing detailed bibliographical guidance to the lichenological
 exploration of each country. This option was preferred in view of the fact
 that most checklists are the first ever to be published for their
 respective countries, but it resulted in two major, critical problems: the
 reliability assessment of literature data, and the selection of sources. It
 is obvious that not all literature records can 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 Spanish literature were checked by Giralt (in litt.) for  the case of
 two genera: Ochrolechia and Rinodina. The number of misidentifications,
 even by "thrustworthy" authors, proved to be very high. In the checklists
 of the present volume a pragmatic approach was taken: they should all be
 considered as the result of a series of "educated guesses" for which their
 authors take full responsibility. Eventually, however, it will be up to the
 reader to judge the reliability of literature data. The essential scope of
 a checklist is that to give the reader a means of doing just that. 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 etc, also be
 taken into consideration ? In this respect, too, the author of the
 checklist is responsible for the mode of selection: the only cogent
 criterion which all authors were requested to adopt is 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.
        Checklists might differ also on account of the degree of exploration of the
 area they cover. For well-explored areas they often represent a basis for
 future updates and a kind of prodromus for a real flora; in the case of
 poorly explored areas they summarize the current state of knowledge, but
 cannot pretend to be exhaustive. The latter is, beyond doubt, the case of
 most checklists of the present volume. The lichenologically best explored
 areas of southern Europe are Italy and the Iberian Peninsula. The numbers
 of known infrageneric taxa are c. 2,200 for Italy (Nimis 1993, and later
 additions), and c. 1,900 for the Iberian Peninsula (Llimona, in litt.).
 Taking into consideration the surface area of the countries covered, the
 only checklist in this volume that may be comparably complete is, perhaps,
 that of the Ukraine. All others should be considered as mere starting
 points for further research.
        The degree of taxonomic knowledge often parallels that of floristic
 exploration. In well-studied areas most infrageneric taxa are likely to be
 relatively well-delimited taxonomically. At the other extreme, a checklist
 may include several names referring to very poorly-known taxa in need of
 critical revision. Thus, the total number of taxa accepted in a checklist
 does not always reflect the actual species diversity of that area, not only
 because of gaps in the floristic investigation, but also due to inadequate
 taxonomic knowledge. Incidentally, further taxonomic research will often
 reduce rather than increase the number of accepted taxa. The checklist of
 Morocco in the present volume accepts several taxa described by Werner that
 were largely forgotten by subsequent authors; many will certainly be
 reduced to synonymy in the future. Their citation in the checklist is,
 however, important, because it will bring these potentially correct names,
 often published in long-forgotten papers, to the attention of specialists.
        Checklists are also expected to be a means of achieving nomenclatural
 stability, at least for some years. In this respect, however, those
 contained in this volume will likely fail. All of course update the
 nomenclature, although with different standards. Lichen taxonomy has
 recently witnessed a dramatic increase in the creation of new genera, on
 many of which the international lichenological community is far from having
 formed a consensus. Thus, the checklist of the Ukraine accepts an extreme
 generic splitting of Parmelia, while the other checklists follow a more
 conservative approach. Many further changes, especially at generic level,
 are to be expected in the near future. It would have made little sense to
 strive at uniformizing nomenclature at this stage. The consensus problem,
 however will present itself anew in a few years' time, in the context of
 the compilation of  an overall checklist of Mediterranean lichens,  and
 will require further discussions at the international level. In this
 volume, the only attempt at uniformization was adherence to the standard
 for authors' abbreviations proposed by Brummitt & Powell (1994).
        To sum up, checklists can have different nature, scope and contents, and
 they should be always judged while considering the situation of floristic
 and taxonomic research that they reflect. In any case, they are a valuable
 tool 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 re-appraisal of
 poorly-known taxa, and for the further exploration of under-investigated
 areas. In this sense, checklists may and should be catalists 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. Their ephemeral value, which is what I
 paradoxically wish to all checklists of the present volume, has an
 interesting implication, to be discussed in the next chapter.
 

Biodiversity on-line

        Checklists are never-ending ventures, subject to continuous updating
 following the developments of current research. In the past, it was
 customary to issue, at certain intervals, checklists with increasing
 "degrees of approximation", but always in the traditional, paper-bound
 form. Recent progress in the fields of interactive data access and
 retrieval now provides scientists with new, powerful tools which can bring
 about a true revolution in data availability. The expansion of the
 Internet, the advent of the World Wide Web, and the development of Web
 servers and browsers that include HTML, have virtually eliminated past
 obstacles to the creation of on-line databases. With a Web server acting as
 a buffer between the database and the network, and Web browsers functioning
 as platform-independent "front ends", network-based database publishing is
 now an easy, cheap and efficient option. Continuous on-line interaction
 among different centres is now possible, a fact that leads on to the
 "publication" of a product that is updated on-line by a continuous stream
 of new information, filtered by the responsible(s) for a given checklist.
 This is exactly what is needed for biodiversity inventories, and what is
 envisaged as the future destiny of the checklists published in this volume.
 

        The simplest approach to database publishing on the Word-Wide-Web is to
 export database views to ASCII text files, marked up as HTML documents, and
 to place them on a Web server for remote access. It is also possible to
 build single-level or multi-level indexes by exporting subsets of the data.
 A slightly more complex approach is to export database views to ASCII text
 files, and access them with the aid of a Wide Area Information Server. Even
 the possibility of remote accessing of simple, flat text files is an
 enormous advance with respect to the past: using the devices of any word
 processing programme, it is possible to search them as a kind of simple,
 limited database.
        Although checklists have been and will continue to be published in the
 traditional form, their continuous updating on the Web provides the
 possibility of a new type of "publication", one that would have not been
 possible in the past and that is particularly adapted for open-ended works
 such as gene-banks and biodiversity inventories. The creation of a working
 space on the Internet for the lichen Med-checklist project will have two
 advantages: (a) facilitating the exchange of information among specialists
 from different countries, (b) making immediately available to the
 scientific community the most up-to-date information on lichen biodiversity
 in southern Europe and the Mediterranean region. The hitherto available
 checklists could be made available in hypertext format in the near future
 and with a relatively minor financial input. The main issue to be solved is
 standardizing the information deriving from different sources, so as to
 allow interaction among different database units, following the proposals
 of the Taxonomic Databases Working Group (TDWG). The biogeographic
 databases originated from our project could be linked with the
 morphologic-taxonomical data handled in the framework of the LIAS project.
 This is a DELTA-based taxonomic database edited by the Botanische
 Staatssammlung München, in collaboration with several international
 centres. This link will eventually permit the production of computerized
 identification keys for any list of lichen species produced from the Lichen
 Med-Checklist databases, which will considerably increase the number of
 potential users of the products of the OPTIMA project.
        There are good possibilities for the checklists of the present volume, and
 those to follow, not merely to be important sources of information
 published in the traditional way, but to become the starting point for a
 wholly new kind of product: continuously updated biodiversity inventories
 available on-line world-wide.

Acknowledgements

        I am indebted to Prof. W. Greuter (Berlin) for his thorough revision of the
 manuscript.
 

References

Arrhenius, O. 1921: Species and area. - J. Ecol. 9: 95-99.
Barreno, E. 1991: Phytogeography of terricolous lichens in the Iberian
 Peninsula and the Canary Islands. -  Bot. Chron. 10: 199-210.
Bolognini, G. & Nimis, P.L. 1993: Phytogeography of Italian deciduous oak
 woods based on numerical classification of plant distribution ranges. -
 J.. Veg. Sci. 4: 847-860.
Box, E. O. 1982: Life-form composition of Mediterranean terrestrial
 vegetation in relation with climatic factors. - Ecol. Medit. 8: 173-181.
Brummitt, R.K. & Powell, C.E. 1994: Authors of plant names. - Kew.
Christensen, S.N. 1989: The lichen flora on Ulmus in a north Greek mountain
 village with an introduction to the literature of Greek lichens. -
 Graphis Scripta 2: 107-113.
Clauzade, G. & Roux, C. 1985: Likenoj de Okcidenta Europo. Ilustrita
 Determinlibro. - Bull. Soc. Bot. Centre-Ouest, nouv. sér., num. spéc.
 7: 1-893.
Clauzade, G. & Roux, C. 1989: Nelikenigintaj Fungoj Likenlogaj. Ilustrita
 Determinlibro. - Bull. Soc. linn. Provence, num. spéc. 1: 1-142.
Crovello, T.J. 1981: Quantitative biogeography: an overview. - Taxon 30:
 563-575.
Daget, Ph. 1977a: Le bioclimat Méditerranéen, caractères géneraux,
 modes de caractérisation. - Vegetatio 34: 1-20.
- 1977b: Le bioclimat Méditerranéen: analyse des formes climatiques
 par le système d' Emberger. - Vegetatio 34: 87-104.
Egea, J. M. & Llimona, X. 1991: Phytogeography of silicicolous lichens in
 Mediterranean Europe and NW Africa - Bot. Chron. 10: 179-198.
Emberger, L. 1943: Les limites de l'aire de végétation
Méditerranéen
ne en France. - Bull. Soc. Hist. Nat. Toulouse 78: 159-180.
Gleason, H.A. 1922: On the relation between species and area. - Ecology 3:
 158-162.
Hafellner, J. 1995: A new checklist of lichens and lichenicolous fungi of
 insular Laurimacaronesia including a lichenological bibliography for the
 area. - Fritschiana 5: 1-132.
Johnson, M.P. & Raven, P.H. 1970: Natural regulation of plant species
 diversity. - Evol. Biol. 4: 127-162.
Kruger, F.J., Mitchell, D.T. & Jarvis, J.U.M. (eds.) 1983: Mediterranean
 Type Ecosystems. - Ecol. Stud. 43.
Kusan, F. 1953: Prodromus Flore Lisaja Jugoslavije. - Jug. Akad. Znanosti
 i Umjetnosti, Zagreb, 595 pp.
Leuckert, Ch. & Poelt J. 1978: Über Nord-Süd Gradienten von Chemotypen
 europäischer Flechten. - Pl. Syst. Evol. 130: 53-77.
Malyshev, L., Nimis, P.L. & Bolognini, G. 1994: Essays on the modelling of
 spatial floristic diversity in Europe: British Isles, West Germany and East
 Europe. - Flora 189: 79-88.
Margaris, N.S. & Mooney, H.A. (ed.) 1981: Components of productivity of
 Mediterranean-climate regions. Basic and applied aspects. Tasks Veg. Sci.
 4.
Nimis, P.L. 1984: Contributions to quantitative phytogeography of Sicily.
 Ist. Correlation between phytogeographical categories and
 environment-types. - Webbia 38: 123-137.
- 1993: The Lichens of Italy. An Annotated Catalogue. - Mus. Reg. Sci.
 Nat. Torino, Monogr. 12: 1-897.
- &  Bolognini, G. 1993: Quantitative phytogeography of Italian beech
 forests. - Vegetatio 109: 125-143.
- & Poelt, J. 1987: The lichens and lichenicolous fungi of Sardinia
 (Italy). An annotated list. - Studia Geobot. 7, suppl. 1: 1-269.
- & Tretiach, M. 1995: The lichens of Italy. A phytoclimatical outline.
- Cryptog. Bot. 5: 199-208.
Poelt, J. 1970: Das Konzept der Artenpaare bei den Flechten. - Vortr.
 Gesamtgeb. Bot. 4: 187-198.
- & Doppelbaur, H. 1956: Über parasitische Flechten. - Planta 46:
 467-480.
Preston, F.W. 1962: The canonical distribution of commonness and rarity. -
 Ecology 43: 186-215.
Quézel, P. 1978: Analysis of the Flora of Mediterranean and Saharan
 Africa. - Ann. Missouri Bot. Gard. 65: 479-534.
- 1985: Definition of the Mediterranean region and the origin of its
 flora. - In: Gomez-Campo, C. (ed.): Plant Conservation in the
 Mediterranean Area. Dordrecht.
Rivas-Martinez, S. 1987: Memoria del mapa de series de vegetación de
 Espana. - Madrid.
Roux, C. 1991: Phytogéographie des lichens saxicoles-calcicoles d' Europe
 méditerranéenne. - Bot. Chron. 10: 163-178.
Scheidegger, Ch. 1991: Phytogeography of the genus Buellia (Physciaceae,
 Lecanorales) in Mediterranean Europe. - Bot. Chron. 10: 211-220.
Seaward, M.R.D. 1976: Performance of Lecanora muralis in an urban
 environment. - In: Brown, D.H., Hawksworth, D.L. & Bailey, R. H. (eds.):
 Lichenology, Progress and Problems. London and New York.
Tukhanen, S. 1980: Climatic parameters and indices in plant geography. -
 Acta Phytogeogr. Suec. 67.

Address of the author:

Prof. Pier Luigi Nimis, Dipartimento di Biologia, Università di Trieste,
 Via Giorgieri 10, I 34127 Trieste, Italy.