White clover (Trifolium repens) can be either cyanogenic, that is, it produces hydrogen cyanide; or non-cyanogenic, that is, it does not produce hydrogen cyanide - VCE - SSCE Biology - Question 21 - 2005 - Paper 1

Grazing action of snails and slugs represents a significant selective pressure. In environments where snails and slugs are prevalent, clover plants that produce hydrogen cyanide (the cyanogenic phenotype) have a survival advantage by deterring herbivory, thereby reducing the population of non-cyanogenic plants.