The terms four-leaved clover and four-leaf clover designate a rare form of clover leaf having four leaflets, regarded as a lucky charm or sign of good fortune—clover is the common name of the species of trefoil (Trifolium, family Leguminosæ), especially Trifolium repens and Trifolium pratense.

It was this superstition that the English author and politician John Melton (died 1640) mentioned in Astrologaster, or, The Figure-Caster. Rather the Arraignment of Artlesse Astrologers, and Fortune-tellers, that cheat many ignorant people vnder the pretence of foretelling things to come, of telling things that are past, finding out things that are lost, expounding Dreames, calculating Deaths and Natiuities, once againe brought to the Barre (Imprinted at London: By Barnard Alsop, for Edward Blackmore […], 1620):

A Catalogue of many superstitious Ceremonies, especially old men and women hold, which were first found out and inuented by Figure-Casters, Cunning Men and Women in former ages, yet to this day are held for certaine and true obseruations.
[…]
That if a man walking in the fields, finde any foure-leaued grasse ¹, he shall in a small while after finde some good thing.

¹ According to the Oxford English Dictionary (2^nd edition, 1989), the term four-leaved grass was used to designate “a four-leaved variety of Trifolium repens”.

The following appeared in The Pennsylvania Packet, and Daily Advertiser (Philadelphia, Pennsylvania) of Thursday 19^th July 1787:

Was stolen from the subscriber, on the 16^th instant, a SILVER WATCH, of a small size, with a piece of red silk in the outside case, and two four leaf clovers under the silk. One of the persons who was concerned in stealing said Watch was about 5 feet 8 or 9 inches high, well made, short dark hair somewhat inclining to curl, a dark brown jean coattee, spotted under jacket, half worn hat; the other had short fair hair, made much like the other, and had on an old white hat and jacket without sleeves, an old pair of dirty tow trowsers; both Irishmen, and marked with the small pox. The Watch had a china face with a steel chain and two blue seals. Four Dollars Reward will be given to any person that will bring it to MARY LIKINS.
Boon’s Island, near Darby, July 17

On Thursday 14^th May 1953, the Daily Express (London, England) considered the following event important enough to merit a four-column headline—boldface is the author’s:

Lucky, lucky girl
SHE FOUND A FIELD OF 4-LEAF CLOVERS
Express Staff Reporter

JOAN ROSINA NOTT, a NINE-year-old schoolgirl with pigtails, whose great-great-grandmother was an Irish colleen, picked NINE four-leaf clovers yesterday—the 13^th.
And she was humming “I’m looking over a four-leaf clover . . . that I’d overlooked before” ² when she found nine of the lucky omens.
At first—earlier in the day—she spied only three and with great excitement rushed home to her parents a lamppost and two trees away in Summers-lane, North Finchley—and tripped over the mat.

So Daddy had a look, too

Mrs. Catherine Nott, her 29-year-old mother, made her stay for high tea, but Joan toyed with the liver and beans.
Finished, she rushed off again but came back disappointed. There were no more. Perhaps daddy would come and look in his carpet slippers? He did.
And then it was that Joan spied the other six in the patch of grass in Downway. And so she had nine clutched in her fist. A fist full of luck.
Today Joan will take one to her teacher. And then she is sending one to the Queen, whishing her luck for the Coronation.
Said Joan: “I don’t think I’ll sleep tonight. I’m so excited and happy. Perhaps it will bring us luck. Daddy went back to work today for the first time after being ill for three years.”

² I’m Looking Over a Four Leaf Clover (1927) is the title of a song by the U.S. lyricist Mort Dixon (1892-1956) and the U.S. composer Harry M. Woods (1896-1970).

Like four-leaved clover and four-leaf clover, four-leaved shamrock designates a rare form of shamrock leaf having four leaflets, regarded as a lucky charm or sign of good fortune.

This superstition is the theme of a song titled The Four-leaved Shamrock, by the Irish miniature painter, author, composer and songwriter Samuel Lover (1797-1868), which appeared as a poem in The Southern Reporter, and Cork Commercial Courier (Cork, County Cork, Ireland) of Saturday 3^rd October 1835:

The Four-leaved Shamrock.

I’ll seek a four-leaved shamrock,
In all the fairy dells,
And if I find the charmed leaves,
Oh! how I’ll weave my spells!

I would not waste my magic might
On diamond, pearl, or gold,
For treasure tires the weary sense,
Such triumph is but cold;

But I would pay [misprint for ‘play’] the enchanter’s part,
In casting bliss around!
Oh! not a tear, nor aching heart,
Should in the world be found.

To worth I would give honour,
I’d dry the mourner’s tears,
And to the pallid lip recal [sic]
The smile of happier years.

And hearts that had been long estranged,
And friends that had grown cold,
Should meet again like parted streams,
And mingle as of old.

Oh, thus I’d play the enchanter’s part,
Thus scatter bliss around;
And not a tear or aching heart
Should in the world be found.

The heart that had been mourning
Oe’r [misprint for ‘o’er’] vanished dreams of love,
Should set them all returning
Like Noah’s faithful dove.

And hope should launch her blessed bark
On sorrow’s dark’ning sea,
And misery’s children have an ark,
And saved from sinking be.

This cartoon was published in The Sketch (London, England) of Wednesday 4^th September 1907:

POPULAR SUPERSTITIONS—III.: PICKING FOUR-LEAVED SHAMROCK FOR LUCK. [Drawn by Tony Sarg ³.

³ Tony Sarg (Anthony Frederick Sarg – 1880-1942) was a German-born U.S. puppeteer and illustrator.

The terms four-leaved clover and four-leaf clover were sometimes associated with even ash (i.e., even ash-leaf), denoting a rare form of ash leaf having an even number (rather than the usual odd number) of leaflets, and thought to bring good luck or to have efficacy in divining future love.

The terms even ash and four-leaved clover were used, in particular, in rhyming incantations—as T. T. Wilkinson explained in the following extract from An essay on the folk-lore of England, &c.; with especial reference to the manners, customs, & superstitions of Lancashire, published in The Preston Chronicle, and Lancashire Advertiser (Preston, Lancashire, England) of Saturday 31^st January 1852:

In Lancashire, and also in some parts of Yorkshire, the even-ash is employed as a charm, in the following manner:—A young woman desirous of ascertaining who her husband will be, pulls an even-ash privately from the tree, repeating, at the moment, these lines:—
“Even-ash, even-ash, I pluck thee,
This night my own true love to see;
Neither in his rick, nor in his rare,
But in the clothes he does every day wear.”
The twig is placed under the pillow at night, and the future husband, of course, makes his appearance in her dreams. Four-leaved clover, has the same effect, for if you get
“An even-ash, or four-leaved clover,
You’ll see your true love before the day’s over.”