FERTILITY AND POLYPLOIDY OF EUPHORBIA CYPARISSIAS IN CANADA

Abstract

E. cypariisias, a European sp. originally introduced into n. America as an ornamental, is now firmly established on roadsides and pastures in e. Canada. The Canadian distribution is mapped from specimens in 3 herbaria. Plants with a somatic chromosome no. of 20 and plants with the number 2[eta] = 40 occur in e. Ontario and adjacent Quebec. The diploid plants apparently never set seed, whereas the tetraploid populations are highly fertile. The cells of the upper leaf epidermis of the tetraploid plants are conspicuously larger than those of the diploid plants. By means of this criterion, the probable chromosome no. of herbarium specimens was detd. The distr. of the diploid and tetraploid plants in Ontario and w. Quebec is mapped. Tetraploid plants are known from 8 locations in this area; 5 of these infestations are serious. It is believed that the sterility of the diploid populations is due to a genic condition which may interrupt normal pollen development.