Mutation Liquid changes your plant when you use it on a plant. Sometimes it changes the species, but more often it changes the variety, and sometimes it changes both. You can use it to find the rarest level of species and varieties. My theory is that the age of the plant determines the effect of the liquid, but I have not done sufficient experiments to support the theory.
For example, I have found that when I use the liquid right after I plant the seed, I will get an arthurium variety of the same species, but if I use the mutation liquid after the plant has matured, I will not get arthurium.