Spotting clover on your pristine lawn might send you scurrying for the weed killer, but if you find a four-leaf clover — well, that's a different story. Universally regarded as a symbol of good fortune (in reality, a horticultural anomaly), the four-leaf clover is often thought to represent "the luck of the Irish." But that's a bit of blarney. The shamrock, or seamróg in Gaelic (meaning "young clover"), is the national plant of the Emerald Isle, but it has only three leaves. And there isn't just one type: Many types of clover are considered shamrocks. Test your friends with this four-leaf–clover trivia over a pint of green beer on Saint Patrick's Day.

The four-leaf clover achieved "lucky" status because the ancient Celtic druids viewed it as a sign of good luck.

According to legend, during the fifth century, Saint Patrick used the shamrock to teach the Celts about the Holy Trinity. The three leaves attached to a single stem represented the unity of the Father, the Son, and the Holy Spirit in one God. If Saint Patrick came across a four-leaf clover, he used the extra leaf to represent "God's grace."

In 1907 a three-leaf clover became the symbol of rural youth clubs across the United States, with each leaf representing one H — for head, heart, and hands. Two years later, the emblem was upgraded to four leaves and H's, the last representing health. By 1924 these clubs had united and became widely known as 4-H, an organization devoted to teaching leadership, citizenship, and life skills to youth in urban, suburban, and rural areas.

In 2002, in Hanamaki, Japan, Shigeo Obara discovered a clover with 18 leaves, a Guinness World Record. (Four-and-a-half times the luck?)

Even luckier: In 2006, on the Kenai Peninsula, in Alaska, Ed Martin Sr. of Cooper Landing found more than a thousand four-leaf clovers in a single day.

One superstition holds that if an unmarried woman finds a four-leaf clover and eats it, she will soon meet her husband. Happy hunting!