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L'ISOLA DI MARETTIMO NELL'ARCIPELAGO DELLE EGADI E LA SUA VEGETAZIONE

1956; Taylor & Francis; Volume: 11; Issue: 1 Linguagem: Inglês

10.1080/00837792.1956.10669652

2169-4060

Eleonora Francini, Albina Messeri,

Ancient Mediterranean Archaeology and History

RIASSUNTO Viene esaminato il rivestimento vegetale dell'isola di Marettimo, appartenente all'arcipelago delle Egadi, ad W della Sicilia. Attraverso allo studio sistematico, corologico ed anatomo-ecologico di un certo numero di piante più rare, viene ricostruita la storia del popolamento dell'isola, le cui tappe principali si sono svolte nel Miocene, iniziando dall'emersione, avvenuta presumibilmente nell'Oligo-Miocene in rapporto ad un movimento orogenetico procedente da W verso E nel bacino mediterraneo occidentale. Viene messa in evidenza la grande importanza che ha per Marettimo l'aver appartenuto per lungo tempo ad un Continente sud tirrenico, posto a N della Sicilia, costituito da tre unità, una orientale, più antica, attraverso alla quale sono avvenuti gli scambi floristici con l'Egeide, una occidentale, di età intermedia, attraverso alla quale sono avvenuti gli scambi con le terre mediterraneo-occidentali, ed una settentrionale, più recente, attraverso alla quale sono avvenuti gli scambi con l'Italia centrale. L'isola di Marettimo si è individuata con la scomparsa di questo continente, presumibilmente nel primo Quaternario. I ponti di terra che nel corso del Quaternario possono averla unita sia con la Sicilia sia con la Tunisia non hanno cambiato essenzialmente l'assetto della sua vegetazione; è rimasta isolata durante l'ultima glaciazione. Viene messo in rilievo che la flora più particolare dell'isola è costituita da piante che mostrano caratteristiche corrispondenti ad un clima ad escursioni piuttosto giornaliere che stagionali. SUMMARY The island of Marettimo, belonging to the Archipelago of the Egades, lies in the western mediterranean, km. 37. West of Trapani, and km. 130 North-East of Cape Bon in Tunisia. It is a rocky little island about m. 700 high, formed by liassic and triassic limestone, with slopes and vertical cliffs, rich with freshwater springs. Its population, living in a small villages, chiefly consists of fishermen. Up to the present time 515 taxa have been reported from Marettimo, 97,6 of which grow also in Sicily, while some of its most interesting entities are unknown from the Sicilian flora (Bupleurum dianthifolium, Brassica macrocarpa, Scilla Hughi, Daphne oleifolia, Periploca angustifolia, Lagurus ovatus var. vestitus, Erodium maritimum) or strictly localized only on the limestone rocks of North-West Sicily (Scabiosa limonifolia, Erica siculo). Among these Buplewrum dianthifolium, Brassica macrocarpa, Scabiosa limonifolia and probably Scilla Hughii are to be considered as endemic of the island (probably paleoendemic). Besides these endemisms we find in Marettimo some peculiar varieties belonging to species present in Sicily (Lithospermum rosmarinifolium var. subuniflorum, Satureja fruticulosa var. coespitulosa, ecc.). The flora of Marettimo is characteristically west mediterranean and the 91 of its species occur in Algeria, while 87 only in Tunisia. The vegetation of Marettimo can be classified as follows: The macchia occupies the higher part of the island, particularly thriving on the western side (North of Punta Libeccio); in the valley enclosed between the main ridge of the island and the lower coastal ridge. This kind of macchia is characterized by Quercus Ilex and Daphne oleifolia. The gariga: some typical communities of which are chiefly composed by Satureja fruticulosa var. caespitulosa and HeUchrysum pend/ulum and grow on the steep east slopes of the island (North of the village), accompanied by a residual group of Pinus halepensis, localized in one station. This gariga can be considered as a mountain type of vegetation. The endemic plants (Scabiosa limonifolia, Bupleurum dianthifoUum, Scilla Hughii, Brassica, macrocarpa) and the most peculiar ones (Dianthus rupicola, Seeeli Bocconi, Iberis semperflorens) find their only habitat on the vertical cliffs with North-North-East exposure, where they grow luxuriantly. A particular study of the most important plants of this flora is presented here. This research has been performed from a chorological and anatomical-ecological point of view as well as by means of the valuation of its degree of specialisation to the habitat of vertical cliffs, in order to reconstruct the history of the plant population in the island. This study led us to assume that the most peculiar flora of the island consists of plants characteristic of tropical-subtropical mountains, where the widest climatic oscillations take place during the day and not during the year (diurnal climate instead of a seasonal one). The ecological categories in which the rare plants of Marettimo can be classified are as follows: 1. Shrubs of evergreen mesophilous type (Figg. 62, 76, 78) probably originated at a low mountain altitude, characterized by a high atmospheric humidity and fog during a part of the day.The most typical representatives (Bupleurum dianthifolium, Dianthus rupicola, SeseK Bocconi) are localized to peculiar habitats, probably from a remote geological period (presumably before the end of the Miocene) and show adaptation to the vertical cliffs which exceeds the most accentuated preadaptation.It is presumed that from this ecological type might have taken origin the evergreen shrubs, expecially of sclerophyllous type, of the mediterranean macchia of today. These plants might have kept some of their original morphological features (scarse conducting power of the wood tissue, general leaf shape) and changed deeply some others (introduction of definite resting periods in the growing process, change of leaf structure from mesophilous to xerophilous type). We find in Scabiosa limonifolia (Figs. 69, 92, 95) a good example of a plant in which the mediterranean features have been reached only in part. According with this incomplete evolution the plant has not been able to spread like the true mediterranean ones, but survives today as a relict on the vertical rocks. Much likely in the same way behaves a mesophilous ecotype of Lonicera implexa (Figs. 107, 108), exclusively bound to the peculiar habitat of the vertical cliffs, for which, being a liane, is well pre- adapted. To the same group belongs Iberis semper flor ens, which shows the same general characteristics as Buplevrum dianthifolium, Dianihus rupicola and Seseli Bocconi, but has a greater tolerance for xerophilous habitats and no adaptation to the vertical cliffs, while it is well preadapted for this habitat.The origin of these plants must be sought for up to the paleogene in the mountains of the mediterranean district, under a tropical climate.These plants show some differences one from the other, owing to the place and time of their origin: Bupleurum dianthifolium whose origin might be brought back to the Betic-Riffan land, in the Western Mediterranean, is the most mesophilous and strictly localized; Seseli Bocconi which could have taken origin in the Corsardinian lands is less mesophilous and less severely localized; Dianthus rupicola of the Egean Continent, besides its mesophüous characters, shows also some other characteristics which let it spread over a rather large area.This adaptation power, which reaches its maximum in Iberis semper florens, is testified by the possibility of living along the sea shores on account of some alophilous features (crassulence).From an anatomical point of view this group of plants is characterized by leaves with a subcuticolar lining of mucillage and by the presence of stomata on the whole leaf surface, probably it may also occur a particular type of hairiness. Prom a taxonomical point of view these species are well defined and more or less isolated.2. Shrubs of evergreen xerophilous type (see for ex. Figs. 102, 116, 118): presumably they originated at a higher mountain altitude, above the persistent fogs, with exposures to longlasting insolation, in opposition to the previous ones.The species are much like those of the mediterranean shrubs of today (stenophillous and microphillous types) and have several features in common with them. They differ from these mainly on account of their deficiency of well defined growth rythm. This characteristic is indicative of a daily climate rather than of a seasonal one. Intermediate stages between this type and the proceeding one may be found. The following plants belong to this category: A sperula rupestris, Lythospermum rosmarin i folium, Satureja fruticulosa, Helichrysum pendulum, Thymus nitidus. As regards their structures these plants show the localisation of the stomata on the underside of the leaf. Two types of leaf can be found: with hairy and hairless upper surface. In the latter the mucilages tend to sink from the outer cell wall (subcuticular) to the inner one, close to the palisade. As regards their taxonomy these species are only feebly differentiated and in some case they must be interpreted only as varieties. They do not show any particular adaptation to the habitat of vertical rocks, for which they are only preadapted.The species mentioned till now are all west mediterranean, but also two east mediterranean plants belong to this group and show some peculiar characteristics; Daphne oleifolia (with leaves of montane Rhododendron type, Figs. 131, 132, 133) is characterized by growth without resting periods, by its fittness to marshy habitats and its defined taxonomical position. Its range covers Colchide, Tuscan-Latial Maremma, besides some relict montane localities. Erica sicula (Figs. 134, 136) is characterized by a restless growth, a rather strong degree of xerophily of the leaf and a high taxonomical differentiation.Evidently we deal with ancient plants, expecially Erica sicula, originated in a well characterized daily climate, without any resting season along the year.3. Herbs of mesophilous type: for this group we have been compelled to base our researches only on chorological data and possibly on the behaviour of these plants in their present habitat. This group comprehends some montane plants chiefly distributed in the Atlas mountains of the North West Africa (Hypochaeris laevigata, Fig. 119, and Ranunculus rupestris, Fig. 126). In this group we find also a bulbous plant (Scilla Hughii, Fig. 124) with mediterranean characteristics and an accentuated degree of mesophily in opposition to the allied Scilla elongata; we find here too Brassica macrocarpa (to be considered much more a big perennial herb than a shrub) with characters of a mesophilous mediterranean plant and a certain degree of alophitic adaptation and finally Lagurus ovatus var. vestitus a primitive entity, compared with the omnimediterranean Lagurus ovatus. All these plants live more or less exclusively on the vertical cliffs, although they do not seem to possess any particular adaptation or preadaptation to the rocky habitat.4. Herbs of mediterranean-atlantic type: we have only one representative of this group: Erodium maritimum. This plant probably originated in the higher altitudes of the mediterranean mountains when the climate of the mediterranean basin was of a tropical type, from there Erodium maritimum spread down and along the atlantic european coasts, where today it has to stand a climate with a scarse seasonal differentiation. This plant shows, like Daphne oleifolia, a certain contact with the marshy habitats. The island of Marettimo must have been part of a « South Tirrenic Continent » at the beginning of the Miocene, and must have become an island at the beginning of the Quaternary period. The South Tirrenic Continent consisted of three main portions (Fig. 154): 1. a paleogenic portion, corresponding to the cristallin mountains of Calabria and Sicily, which acted as a bridgehead for the invasion of egean plants.2. an oligocenic-miocenic portion corresponding to the calcareous west Sicily and therefore including also Marettimo, which acted as a bridgehead for the invasion of the plants coming from the Riffan-Betic lands and from Corsardinia and Algeria.3. a pontic portion which extended from Sicily to the central italian peninsula. Marettimo, owing to its position at the south western point of this South Tirrenic Continent is particularly rich in western mediterranean relicts. The colonisation of Marettimo took place most probably during the Miocene (Fig. 153). During the greatest sea ingressions Marettimo probably became and island of an Archipelago, successively at the time of the greatest land emersion Marettimo became once more part of the above mentioned Continent, and took connection with the North Western lands. During the Pontic the mountains of Marettimo probably were surrounded by a lagoon, somehow like Monte Argentario today, in the Tuscan Maremma. The survival of several peculiar species in Marettimo has been possible chiefly thanks to the ecological-geographical conditions of the island. Being a small island well isolated from the main land, Marettimo has a very even climate. The underground circulation of waters is particular abundant and the fresh waters seeping from the crevices weakens the effects of summer dryness. Finally the geographical isolation of Marettimo probably dating from the Calabrian has prevented the ingression of a more recent flora. The land bridges which could occasionally have risen during the glaciations probably have not been much efficient in this respect. The vegetation of Marettimo probably has not changed in its general outline since the time of its isolation from the main land; this is shown also by the fact that its relict species are scattered in different habitats and not only limited to typical refuge stations such as limestone cliffs. Exspecially important in the preservation of the peculiarities of this vegetation must have been the isolation of Marettimo during the interglacial periods.