“…The haploid chromosome complement of P. nigra is n = 8 (Benazzi, 1963;Benazzi & Benazzi Lentati, 1976;Le Moigne, 1962), and this basic chromosome number has been documented in individuals from several European localities (Lepori, 1949(Lepori, , 1950(Lepori, , 1954a(Lepori, ,b, 1955, including Italy (Canovai, 1989;Canovai & Galleni, 1988;Canovai et al, 1985), southern Sweden (Melander, 1963), the Netherlands (De Vries, 1985 and Van der Velde), and France (Dutrilleux & Lenicque, 1971;Le Moigne, 1962;Lepori, 1954a). In addition to the basic karyotype, supernumerary (B) chromosomes (Jones & Rees, 1982) of variable morphology (Canovai, 1989;Canovai et al, 1985) have been described in diploids and polyploids from different populations.…”