Chromosome numbers of the 59 species of Eucalyptus L'Herit. (Myrtaceae)

The paper presents the results of the chromosomal counting of 59 species of genus Eucalyptus among which 55 are newly examined. All these species possess 2n = 22 including the four species for which the numbers 2n = 20, 24 and 28 have been reported. The number 2n = 24 previously raported in 9 species appears to result from a break of the chromosome first pair very often observed in the Eucalyptus in the metaphase and especially premetaphase stage. Although some contradictory cases of aneuploid have been reported in the literature, the large homogeneity of the chromosome number 2n = 22, now known for 135 (33.5%) distinct species, makes the genus Eucalyptus to be considered as a vast caryologic continuum who probably adopts a process of evolution based fundamentally on chromosome alterations.