From MSNBC:

Irish shamrock a load of blarney, some say

St. Patrick’s Day hype aside, botanists say, nothing special about clover

DUBLIN, Ireland - For one week a year, nursery owner Cecil Geddis is knee-deep in shamrocks, the delicate three-leafed plant that people the world over associate with Ireland and St. Patrick’s Day.

“You have to move fast in this business. Nobody wants to buy a shamrock on March 18,” said Geddis, whose nursery has produced 80,000 shamrock plants, most shipped out in cartons bearing leprechaun decorations and labeled: “Authentic shamrock — grown in Ireland.”

(more here)

I still don’t get it,  what the heck is the difference between a “Shamrock” and a “Clover” ?