Often male sterile in field, highly seed and pollen sterile, selfing can give a fertile polyploid May produce 100 % anthers in the greenhouse Crosses can be made with difficulty M. cardiaca Gerarde ex Baker. Scotch spearmint cultivar. Often male sterile in the field, but may produce 100% anthers in the greenhouse. Highly seed and pollen sterile, but crosses can be made with difficulty. Functional gametes are likely to contain all the chromosomes and selfing can give a fertile polyploid