Chromosome Numbers inZamia(Cycadales)

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Abstract
Chromosome numbers of 14 species of Zamia range from 2n = 16 to 2n (3n?) = 27. West Indian zamias have the most symmetrical karyotype (12M + 4S) and probably are the least primitive members of the genus. Most Central and South American zamias have higher- numbered karyotypes (2n = 18 to 2n = 27). The greatest variation in chromosome numbers for any species within the genus occurs in Zamia chigua (2n = 22, 24, 25, 26), the latter being 4S + 22T. Those species judged to be the most primitive on morphological and ecological bases also possess the higher numbers of telocentric chromosomes; those judged the most ecologically and morphologically specialized (West Indian forms and the epiphytic Z. pseudo-parasitica) have the more symmetrical, lower-numbered karyotypes. In consequence, it is suggested that the trend in karyotype evolution in Zamia has been in the direction of increasing symmetry produced by fusion of telocentric chromosomes.