Ireland is suffering from a "severe shamrock shortage" this year, say local botanists. What's behind the new scarcity of Ireland's national plant, and how might traditionally minded St. Patrick's Day revelers—who favor a shamrock pinned to the lapel—be affected? Here, an instant guide to the great shamrock shortage of 2010:

What's a shamrock, anyway?
The shamrock is a specific variety of three-leaf clover, Trifolium dubium. While strongly associated with Ireland, it actually grows throughout the British Isles and northwest Europe.

Why does the shamrock have to do with St. Patty's Day?
In A.D. 400, St. Patrick used the shamrock to explain the concept of the Holy Trinity—Father, Son, and Holy Spirit—while converting the druidic Irish to Christianity.

Why is there a shortage in Ireland this year?
It's the result of a one-two punch, scientists say: Development and agriculture have gobbled up much of the plant's native habitat in Ireland's "unimproved grasslands," while a brutally cold local winter has stunted the growth of the remaining shamrock.

Will the shortage crimp St. Patrick's Day celebrations?
Not really—revelers can easily switch to such look-alike plants as white clover (Trifolium repens) or black medic (Medicago lupulina). These "bogus shamrock plants" have a wider native habitat and are still abundantly available.

Will Americans be affected?
Unless they're searching for shamrocks sourced directly from the Ireland, Americans can rest easy. And, fortunately, the Irish-grown stock is sufficient to meet the needs of Irish Prime Minister Brian Cowen, who will be presenting Obama with a bowlful of shamrock cuttings at the White House St. Patty's ceremony.

Sources: Irish Central, Irish Times, Landscaping, Catholic Online, National Geographic