12 - Studia Geobotanica. An international journal - Vol. 12 (1992)

KARYOLOGY OF SOME CRITICAL TAXA ON CALAMINE SOILS (CAVE DEL PREDIL, JULIAN ALPS, ITALY). The results of chromosome counts and analyses of karyotype asimmetry on polymorphic taxa growing on calcareous and metalliferous soils and on tailings of a zinc and lead mine are reported. The investigated taxa are: Biscutella laevigata L. subsp. laevigata (2n=36); Dianthus sylvestris Wulf. (211=30); Erysimum sylvestre (Cr.) Scop. (2n=l4); Minuartia venia (L.) Hiern. (211=24); Viola tricolor L. subsp. subalpina Gaudin (211=26) and its var. raiblensis Lausi et Cusma (2n=26) of the same subspecies; Alyssum wulfenianum Bernh. (2n=16); Thlaspi cepaeifolium (Wulf.) Koch subsp. cepaeifolium (2n=14). New chromosome numbers are reported for Alyssum wulfenianum and for Thlaspi cepaeifolium in its locus classicus.

MORPHOLOGIC AND CYTOTAXONOMIC INVESTIGATIONS ON SOME TAXA OF HELLEBORUS SECT. HELLEBORUS IN THE FRIULI-VENEZIA GIULIA REGION (NORTHEASTERN ITALY) AND ISTRIA On the basis of morphometric, histoanatomic and cytotaxonomic analyses, the populations of Helleborus of the Trieste Karst region (North-Eastern Italy) and Istria with smaller floral diameter (4.4-4.8 cm), currently treated as H. multifidus subsp. istriacus, are here included into the H. odorus complex.

A nomenclatural revision of the Illyrian beechwoods of Slovenia, Croatia, Southwestern Hungary, Southern part of Carinthia (Austria) and Northeastern part of Italy (Veneto and Friuli-Venezia Giulia) is presented. Some beechwoods from Bosnia and Herzegovina as well as Montenegro have also been considered. The names of the Aremonio-Fagion, 4 suballiances as well as 22 associations have been revised, nomenclatural types selected and copious synonyma assigned.

Four rnain successional stages in the abandoned rnowed meadows belonging to Junco Molinietum association are evidenced by means of a structural study of the colonizing tree species, and especially far the black alder. The graduai decrease in soil humidity and the forrnation of high tufts of Molinia make possible only the vegetative propagation of the black alder and the penetration of rnesophilous tree species. Under the alder wood, corresponding to the third stage of the succession, natural renovation is totally lacking. However, the abundance of maple, ash and oak seedlings preludes an evident dynamism towards an Aceri-Tilietum forest association.