The name shamrock comes from Irish seamróg which is the diminutive of the Irish word seamair óg and simply means "young clover".
At most times, Shamrock refers to either the species Trifolium dubium (lesser clover, Irish: seamair bhuí) or Trifolium repens (white clover, Irish: seamair bhán). However, other three-leaved plants—such as Medicago lupulina, Trifolium pratense, and Oxalis acetosella—are sometimes called shamrocks.
Those are the guys who messed it all up with a bad arbitrary rule. Anyway, people ushered in a new millennium on 1 January 2000, and no one really cared about 2001. Is the 19th century 1801-1900 and the 1800s 1800-1899? It sounds so silly! So I say we edit history and push everything back a year. World War I is now from 1913-1917. The War of 1812 now started in 1811! Y2K is now 1999! Who's with me?