Thousands of people don a shamrock on St Patrick's Day but how many know their trifolium repens from their oxalis acetosella? BBC News Online unearthed the truth rooted behind the myth.
The shamrock is an iconic image
It is commonly believed the shamrock is a clover - the Gaelic word seamrog means "little clover" - but the botanical world is not so sure.
There is much debate about which species is the real thing and some of the likely candidates are not even classified as clover.
This confusion is partly down to the mythology of the shamrock and the different representations that have appeared in Celtic artwork through the centuries.
According to Irish legend, the druids in Ireland looked at the shamrock as a sacred plant because its leaves formed a triad. Three was a mystical number in the Celtic religion.
Then St Patrick, who was thought to be born in Wales, used the shamrock in the 5th century to teach people about Christianity as he travelled around Ireland.
He told people that each of the three leaves illustrated the Father, the Son and the Holy Spirit of the Holy Trinity.
Old Irish manuscripts make no reference to this in connection with St Patrick, so this is likely to be pure mythology.
WHICH IS THE TRUE SHAMROCK?
trifolium dubium (lesser trefoil) 46%
trifolium repens (white clover) 35%
medicap lupulina (black medick) 7%
oxalis acetosella (wood sorrel) 5%
trifolium pratense (red clover) 4%
Source: Survey of Irish people by Charles Nelson, 1988
According to Nathaniel Colgan, the botanist and author of The Flora Of County Dublin in 1904, people even ate the shamrock in times of famine.
In the 19th century it became a symbol of rebellion against the English and began to be strongly associated with Irish identity. Apparently anyone wearing it risked death by hanging.
Botanist Charles Nelson carried out a shamrock survey in 1988 for his book Shamrock: botany and history of an Irish myth.
He asked Irish people to collect what they imagined to be shamrocks and send them to him.
The top five species can all be found in northern Europe and all but two are forms of clover. Only the trifolium can strictly be called clover.
The trifolium dubium, which can be found throughout the British Isles, was the most common in Dr Nelson's survey.
It is an annual plant which grows to 25cm in height, and can be bought in seed packets.
The trifolium repens, or white clover, is commonly found on lawns as a wildflower.
James Armitage of the Royal Horticultural Society in Wisley told BBC News Online the five species were all similar looking plants.
"They have this trifoliate leaf so if you are not an expert they can be easily confused.
"The shamrock is known from artwork and not from an exact botanical representation, so to fix a species to it is quite difficult.
"The plant itself is not particularly fascinating. It's slightly weedy and grows in grassy areas and open ground."
He said there was a similar conundrum surrounding the Scottish thistle because no one was sure what species it was meant to represent.
The four-leaf clover is said to be a lucky charm and it comes about when the plant mutates.