What is a shamrock?

Ah, 'tis a fine day to answer such a question.  In the local garden shoppe there were lots of quite handsome "shamrocks" for sale, and TPP has a couple of Irish women who like to be remembered with a little something on St. Patrick's day, and neither are fond of Irish whisky with a pickle juice chaser (no joke).  If anything will ruin the taste of good whisky, it's pickle brine; it can even ruin the taste of not so good whisky. But back to topic. The plants were Oxalis, wood sorrel. While a handsome enough plant this is not the true shamrock, if indeed, such a plant exists.  The whole idea of the shamrock was to commemorate the trinity via a plant with 3 leaflets, the seamrog, (accent mark in there somewhere), a common name for a clover.  Quite a few clovers have leaves with three leaflets and are appropriately names Trifolium.  At least 2 species in Ireland could be considered the true shamrock, but it certainly isn't wood sorrel.  And of course if lucky enough you may find one of those leaves with a development abnormality, 4 leaflets.  Happy St. Patrick's Day.  Oh, no wood sorrel for Mrs. Phactor, but some really bright and cheerful phony peonies for her office.