No abstract

Together with a number of collaborators I have made a detailed investigation of the differentiation of the flora and the distribution areas in one of the Aegean regions, the Cyclades. In this paper a few points of general interest concerning the phytogeography of this region are discussed, e.g. the „natural”︁ vegetation, the distribution of rock plants, the explanation of the „Cycladian gap”︁ in the distribution of some species.

Summary When trying to answer the question whether the effects of genetic drift have evolutionary significance, we must keep in mind that a local population is normally a dynamic system, changing in size, splitting into minor entities, or merging into larger complexes. Most populations have certainly been small for longer or shorter periods, and hence the role of genetic drift must not be neglected. The main role of genetic drift in the complex processes involved in the evolution of plants may be (1) the introduction of genetic factors, which are primarily non‐adaptive, (2) the rapid fixation of genetic changes, and (3) the breaking down of rigid gene blocks. Generally speaking a population may be said to be in a selective phase when it is large and in a creative phase when it is small.

Together with a number of collaborators I have made a detailed investigation of the differentiation of the flora and the distribution areas in one of the Aegean regions, the Cyclades. In this paper a few points of general interest concerning the phytogeography of this region are discussed, e.g. the „natural”︁ vegetation, the distribution of rock plants, the explanation of the „Cycladian gap”︁ in the distribution of some species.

The taxa cytologically studied in the Elymus (Agropyron) elongatus complex included three subspecies of E. elongatus, i.e., ssp. elongatus and ssp. haifensis (2n= 14) and ssp. flaccidi‐folius (2n = 28), as well as E. varnensis (2n = 70). A brief taxonomic treatment of these different types is presented. Differences in karyotype were observed between materials of ssp. elongatus that have different origin as well as between ssp. elongatus and ssp. haifensis. Both subspecies have heteromorphic chromosome pairs. In the case of ssp. flaccidifolius, it was possible to arrange the chromosomes in seven groups of four. These groups correspond to the seven pairs of the diploid subspecies which indicates the likelihood of an autopolyploid origin of the tetraploid subspecies. That the chromosomes in most of these groups could be further differentiated into pairs suggests that “intervarietal” crossings have also been involved. Meiosis was studied in ssp. elongatus and flaccidifolius. The satellited chromosomes detectable in E. varnensis were few; they represent, however, types that are found in the three subspecies of E. elongatus. This indicates that the two species are interrelated.