I should preface this with a trigger warning because there is a graphic historical quote below.
Having grown up with one foot in the Irish diaspora I have an extreme fondness for both the shamrock and the four-leaf clover. You can find them hanging around my house year-round, but I especially love pulling more out during late February when I am tired of the brown of winter.
You might be wondering what makes a shamrock different than a four-leaf clover? My answer is genetic mutation. You can read more about that here. Even though it has been a subject of much debate over the years, they are the same plant.
There really isn’t as much confusion as people let on. It’s just a good marketing hook. I even wrote an article about it myself several years back at the request of an editor. A girl must eat, you know? If you want to prove this to yourself do a Google Book search for seamróg limiting your search to books published before 1850.
The Irish words seamroge and seamróg are diminutive forms of seamar meaning trefoil or three-leaved. We see this diminutive in the Irish names of many plants. Seamrag-mhuir is a type of yellow loosestrife, and seamsog is the Irish word for wood sorrel (Oxalis spp.) In 1904, Dinneen’s famous dictionary defined the seamróg as “the shamrock; trefoil, clover; an herb that brings luck to the bearer” and seamsóg as wood sorrel.
The word shamrock is an anglicized version of the Irish word seamróg, so I will use that spelling for the rest of this article as I am not a fan of colonization. For what it’s worth it’s not just the Irish who think four leaf clovers are lucky. Seamarag is the Scottish Gaelic spelling Carmichael tells us that those clovers that grow a fourth leaf are known as the seamarag nam buadh (shamrock of luck) The Scottish Clan Sinclair claimed it as their emblem and wore it on their cap or lapel.
While used medicinally, they were not uniquely Irish medicine. In 1633, Gerard wrote that that the meadow varieties of Trifolium family were collectively referred to as seamróg in Irish and trefoils by the English. “There be divers sortes of three-leafed grasses…first, of the common meadow Trefoiles, called in Irish Shamrocks.” The Synopsis Stirpium Hibernicarum simply listed shamrock as Trifolium as well but expanded on this saying that “White Flowered Meadow Trefoyls are called in Irish Shamrocks.” K’Eogh’s Irish herbal contained shamrock as the Irish name of the White flowered Meadow Trefoil with the Latin name Trifolium Pratense album.
I could just leave this right there but since that’s not considered to be “the” species modernly, I thought it might be interesting to try to take you some of the history of the seamróg.
Some confusion seems to have started in 1707 Edward Lhywd an published an Irish-English dictionary in which he erroneously replaced the word seamsog (the Irish name for wood sorrel) with the word seamróg. He clearly knew better he had written a letter once saying that “shamrug was our common clover?”
This entry was cited often during a centuries long debate in which English people identified the shamrock as oxalis. Pharmacist and amateur historian Henry Wellcome insisted “wood sorrel (Oxalis acetosella) which is also indigenous to Ireland, is the plant called ‘shamrog’ in the old herbals.”  This makes me wonder if Wellcome read any of the old herbals he collected?
It’s particularly annoying because Irish natives had been trying to push back against that identification for some time. Thomas Porter of the Ulster Archeological Society replied, “If we take the practice of the Irish in selecting a sprig of shamrock to decorate their hats on the 17th of March for our guidance as to the species, I should be more in lined to say that the white clover (Trifolium repens) is the genuine.”
In 1893, Irish naturalist Nathaniel Colgan tried to prove the identity of seamróg as Trifolium repens, by identifying plants he bought on the streets of Dublin. He collected 33 plants; 19 were T. repens, 12 were T. minus (syn: T. dubium) and the remaining two were Black Nonsuch (Medicago lepulina).
It appears Colgan stumbled upon a competition that Trifolium repens was destined to lose. 15 years later Michael Moloney wrote “Two of these [native clovers] dispute the title of national emblem. The claimants are Trifolium Repens and Trifolium Dubium vel Minus. Both share the honour of being worn on St. Patrick’s Day, but as the leaves of T. Repens are marked with a white spot and the smaller forms are preferred, T. Dubium is undoubtedly the Shamrock of to-day.”
That seems to have taken hold because you certainly don’t see the white markings on modern depictions. My Irish friends tell me that today Trifolium dubium is marketed as the “true seamróg.” The plant’s modern Irish name is seamair bhuí (yellow clover) while the name seamair bhán (white clover) refers to Trifolium repens.
This brings me to explaining the popularity of seamróg in Ireland. There’s a lot that could be said here about romantic nationalism and the Celtic revival. There is much folklore that is “historical” only in the sense of a nation that re-invented itself in an effort to escape colonization and to write about that would require a book.
You are likely to have read about St. Patrick using the seamróg to teach the Trinity to the Druids of King Laoghaire. There’s no substantiation of these stories as they do not appear in any of the official histories (called hagiographies) written about the saint. That particular Irish story seems to have surfaced at some point in the early 18th century. 
St. Patrick is also very unlikely to have driven away any snakes with a shamrock, as there were never any snakes in Ireland. It is also unlikely that snake is a metaphor for pagan. While this is a bit of conjecture, we do know that trefoil had been associated with repelling serpents since Pliny wrote that “serpents are never seen upon trefoil.” Older Irish scholars theorize that an Irish storyteller passed this story along in an Irish version, as happened with many older customs.
You should know most of what is written about pagan Ireland is based on monastic invention. Pushing back against “Celtic fakelore” is not the purpose of this blog. If you want to read a good account of what we know about St. Patrick and Irish pagans. I recommend this scholar’s work. https://voxhib.com/
Regardless of whether these stories are based in fact, they became part of the oral narrative of the Irish people and the Irish diaspora, and that counts for something, too. There’s nothing wrong with a bit of green plastic hat fun occasionally. It is clear from folk music and poetry that the shamrock holds a special place in the Irish heart.
It was long before the shamrock, dear isle’s lovely emblemThe folk song “The Bard of Armagh”
Was crushed in its beauty ‘neath the Saxon lion’s paw…
Wearing a shamrock on St. Patrick’s Day has been a tradition for a good long time now. An 1827 entry in Ó Súilleabháin’s diary assures the reader that there is a “seamróg in every hat on St. Patrick’s Day.” In the 1930s the celebration seems to have picked up a bit, and they didn’t forget to include their family who had left Ireland.
Everyone who can wears green- a green ribbon or a badge tied around a shamrock branch. It is a national holiday and everyone has a free day. That night the men “drown” the shamrock in a glass of whiskey. They dip the shamrock into the spirit and then they drink it. If we have friends over the sea we send them boxes of shamrock to wear on that day.The Schools’ Collection, Volume 0742, Page 307
You can read a story about the Presentation Order in the Schools collection. It was about ten miles from the farm I grew up on. It seems the words of Mother Hennessy “He who feeds the birds of the air will not forget the Irish exiles” are known on both sides of the sea.
It’s an interesting phenomenon… the Irish diaspora. I can only conjecture at what it is that causes us to seem “more Irish than the Irish themselves” to borrow a phrase. Having grown up in an area where Catholics used to host clergy from Ireland like they were royalty and churches routinely passed the hat for causes “back home”, I think that the Irish interest in the souls across the sea had something to do with it.
The shamrock probably won a permanent place in Irish hearts when it became political. The Volunteer militias formed in Ireland when the English went to fight the Revolutionary war in America adopted the seamróg as their emblem. Members of this group broke off to form the Society of the United Irishmen, an organization whose goal was to drive the English colonizers out of Parliament and presumably Ireland. They adopted green as their color and their supporters would tuck a shamrock in their “caubeen” or pin them on their clothes.
During the rebellion they led in 1798 anyone wearing green was dealt with harshly. There are eyewitness accounts of those “sickened to witness Ancient Britons cutting the haunches and thigh off the young women for wearing green stuff petticoats.” Wearing “an emblem of affection to Ireland” was outlawed and doing so would “subject a man to imprisonment, transportation, the rope or the bayonet, and expose women to the brutal insults of the common soldiery”. Many Irish people were forced from their homes to faraway lands, or worse, for wearing the seamróg, and they kept wearing it wherever they landed.
“The Wearing of the Green” is a folk song that dates to the Irish Rebellion of 1798.
Oh, Paddy dear! and did ye hear the news that’s goin’ round?
The Shamrock is forbid by law to grow on Irish ground!
No more St. Patrick’s day we’ll keep; his color can’t be seen.
For there’s a cruel law agin’ the Wearing o’ the Green!
When Queen Victoria was trying to rebuild relations with Ireland, she gifted Irish regiments with sprigs of seamróg on St. Patrick’s Day, which assured that the seamróg would remain the symbol of Irish nationalism.
So hopefully this gives you a little more insight as to why such a tiny little plant has the heart of the Irish and their diaspora, wherever in the world they may be. For many the plant symbolizes the spirit that inspires colonized peoples to fight for freedom from the oppressor.
 Shaw, William. (1780). A Galic and English dictionary: Containing all the words in the Scotch and Irish dialects of the Celtic, … (Vol. 1–2). W. and A. Strahan.
 Dinneen, Patrick Stephen, ed. Foclóir Gaedhilge Agus Béarla. Dublin, Ireland: M.H. Gill & Son, LTD., 1904. 584.
 Carmicheal, Alexander. (1928). Carmina Gadelica (Vol. 2). Edinburgh, Scotland: Oliver and Boyd.109.
 Cleomenes, C. (1823). Scottish Clans. The Gentleman’s Magazine, 93, 216.
 Gerard, John. (1633). The herbal or general history of plants [1975 Reprint]. (Hill, Thomas, Ed.). New York, NY: Dover Publication. 1185.
 Threlkeld, C., & Molyneux, T. (1726). Synopsis stirpium hibernicarum alphabetice dispositarum. … Being a short treatise of native plants…with their Latin, English and Irish names. Dublin, Ireland: S. Powell. TR.
 K’Eogh, J. (1735). Botanalogia universalis hibernica: or, a general Irish herbal … Cork, Ireland: George Harrison.p 124.
 Colgan, N. (1896). The shamrock in literature: a critical chronology. The Journal of the Royal Society of Antiquaries of Ireland, 6(3), 211–226.
 Frazer, W. (1894). The shamrock: its history. The Journal of the Royal Society of Antiquaries of Ireland, 4(2), 132–135.
 Wellcome, Henry S. Medicine in ancient Erin; An historical sketch from Celtic to mediaeval times. London, England: Burroughs, Wellcome & CO., 1909. 61.
 Porter, Thomas. (1857). The shamrock. Ulster Journal of Archaeology, 5, 12–20.
 Colgan, N. (1893). The shamrock: a further attempt to fix its species. The Irish Naturalist, 2(8), 207–211.
 Colgan, N. (1896).
 Plinius Secundius, Gaius. (1856). The natural history of Pliny. (Bostock, John & Riley, H.T., Trans.) (Vol. IV). London, England: H. G. Bohn 375.
 Martin, W. G. W. (1895). Pagan Ireland; an archaeological sketch: a handbook of Irish pre-Christian antiquities. London, England: Longmans, Green, and Company.
 Ó Súilleabháin, Amhlaoibh. (1979). The diary of Humphrey O’Sullivan, 1827-1837 a translation of Cín lae Amhlaoibh. (de Bhaldraithe, Tomás, Trans.). Dublin, Ireland: Mercier Press.
 Anastas Ní Catháin. ‘The Presentation Order in Iowa Foundation from Mooncoin’. The Schools’ Collection Dúchas © National Folklore Collection, UCD Is Licensed under CC BY-NC 4.0. 0841 (c 1938): 19–30.
 Coogan, Tim Pat. The Famine Plot: England’s Role in Ireland’s Greatest Tragedy. St. Martin’s Press, 2012. 16.
 Irish Music Daily. ‘Wearing of the Green – Irish Nationalist Song’. Accessed 6 March 2020. https://www.irishmusicdaily.com/wearing-of-the-green.