Revisione tassonomica delle querce caducifoglie della Sicilia

Abstract

Taxonomical revision about the deciduous oaks of Sicily.— On the basis of literature, herbarium and field investigations, a survey on the species of deciduous oaks occurring in Sicily is presented. A morphological description fitted with drawings and completed by some chorological and ecological observations is reported for each species. Finally it is emphasized that the phenotypical variability observed in Sicily within the Q. humilis group, even if let to consider the S.Thyrrhenian area as a probable speciation center of the group, on the other hand should also be related to the deforestation, which favoured the genetic mixing among the populations. The present study brought to the recognization in Sicily of 9 species, well distinguished by morphological, ecological and phenological features. They are: Q. cerris, well known species, in Sicily widespread in mountain sites of the north-eastern part of the island; Q. gussonei, endemic closely related to the previous species, occurring in the sub-mountain belt of N-Sicily, where it is localized on siliceous substrata; Q. fontanesii, probably an hybrid between Q. gussonei and Q. suber and distributed within the area pertaining the former parent; Q. petraea, in Sicily represented exclusively by the new subsp. austrotyrrhenica, very rare Sicilian-Calabrian endemic localized in fresh and foggy valleys within the beech belt; Q. congesta, Q. virgiliana, Q. dalechampii, Q. amplifolia, and Q. leptobalanos, all belonging to the Q. humilis group. In particular: Q. congesta is an acidophilous and orophilous species endemic of Sicily, Calabria and Sardinia, mainly characterized in having small and regular bark-ribs, an extremely short fruiting axis bearing several fruits having a small cyathiform cup covering not more than 1/4 of the acorn, and vey small and finely imbricate scales; Q. virgiliana is mainly distributed in the basal and sub-mountain belt, and has a bark quite similar to the previous species but as a main feature it presents very big acorns covered up to 1/2 by an hemisphaeric-barrel-shaped cup having a very irregular border and uniformely silky scales; Q. dalechampii is an orophilous species characterized by very prominent thick bark-ribs, acorns covered up to 2/3 by an hemispaeric-ogival cup with a regular border and long scales silky at the basis, carinate and dark at the tip; Q. amplifolia is the most thermophilous among the sicilian deciduous oaks and has a bark very similar to the previous species but the very big acorns covered up to 1/4 by an cyathio-barrel-shaped cup having humped subglabrous or sparsely hairy scales make unmistakable this species; Q. leptobalanos is a very localized sicilian endemic growing exclusively on siliceous incoherent soils in the mountain-belt of NW-Sicily, it is mainly characterized by a greysh bark with small and regular ribs and by the production of a great number of small fruits bearing on generally long axis. Finally it must be stressed that Q. sicula, quoted from Sicily by several authors, must be considered a phantom species, since it is described on a specimen taken from plant cultivated in the Botanical Garden of Palermo, probably to be ascribed to Q. canariensis; while Q. minaae is likely an hybrid form having an uncertain taxonomical value. Some other species, even if reported for the Sicilian flora, must be excluded from it, since their mention is mostly due to a mistake in the specimens identification, as in the case of Q. crenata, Q. humilis, Q. robur, Q. frainetto, Q. brachyphylla.