The books all say that there are lots of different types of clover that get called shamrock. And each sort is the one and only real shanmrock and all the others are strange substitutes made by poor people who can't get hold of the right sort.

And the real stuff for me is the sort that the cousins always used to send us over every March, and it's got very small leaves and is dark green and grows in wet conditions, and no matter how good the roots might be, if you try planting it over in England it dies on you.