The Science of the Shamrock

Happy St. Patrick’s Day! Everyone else may be drinking at the pub and kissing everyone else that claims to be Irish today, but let’s talk about the foliage behind the festivities. The patron saint of Ireland used the typical shape of the shamrock as an illustration of the Holy Trinity. The Latin name of the white clover genus, Trifolium, literally means three leaves.

Spot the four-leaf clover Credit: Kristie Phillips

Spot the four-leaf clover
Credit: Kristie Phillips

More four-leaf clovers Credit: Kristie Phillips

More four-leaf clovers
Credit: Kristie Phillips

As symbolic as the common foliage form may be, we all know that the four-leaf clover is a symbol of good luck. This is because the four-leaf variety is quite rare (about 1/10,000). I am not a lucky person and have never personally found a four-leaf clover. All of the pictures of 4+-leaf clovers in today’s post are from my friend Kristie Phillips* whose special superpower is finding rare clovers with more than three leaves. Check out this link for more science-based tips on finding your own four-leaf clover. If you are just interested in the statistics behind finding a four-leaf clover check out these posts. Even rarer are clovers with more than 4 leaves. The world record for most leaves on a shamrock is 56!

Five-leaf clovers Credit: Kristie Phillips

Five-leaf clovers
Credit: Kristie Phillips

You may be wondering what the underlying reason is for these deviations from the typical three-leaf form. You are not alone. Other plant scientists have had the same question. They have been working on determining the genetic basis of leaf number and other valuable ornamental traits in clover. This has been slow going because clover is an allotetraploid, which is a hybrid that has four times the number of chromosomes of 1n gamete cells. With these complex genetics, clover prefers to outcross giving a wide range of phenotypic forms. Surely, there is a genetic component to the multiple leaf form of clover- some rare recessive gene that is infrequently unmasked to give four-leaf clovers. Scientists were able to map this trait along with a few other desirable ornamental traits. This was a real breakthrough for breeders that are seeking to enhance the frequency of these traits in clover used as ornamental bedding plants. Note, that genetics isn’t the entire answer because environmental conditions also contributed to the frequency of the four-leaf foliage variety. Will the four-leaf clover be any less lucky once its frequency is increased to 1/100 or 1/10? I’m not sure, but maybe I’ll finally be able to find one.

Even more than six-leafed clover Credit: Kristie Phillips I told you she had a superpower!

Even more than six-leafed clover
Credit: Kristie Phillips
I told you she had a superpower!

However, an exact gene controlling this trait has not yet been identified, but scientists may not be that far away from tracking it down. The genome for red clover was published earlier this year and I’m sure it won’t be long before breeders and scientists will correlate the markers used by breeders to the assembled sequences within the genome. The molecular mechanism for four-leaf clovers is still a mystery for now, but understanding how this works will provide new insights into plant development. Breeders have long sought after ways of controlling patterns in complex leaves for ornamental plants and the secrets of the shamrock may prove useful toward attaining this goal.

These types of scientific discoveries make for good blog fodder on days like today, and maybe I’ve tricked some of you into learning some plant science**. However, some of you out there may be wondering if your tax dollars were really spent determining what makes clovers have four leaves. Before you get all grumpy cat on scientific research spending, let’s talk about how important clover really is. Even if you could care less about ornamentals (and the market value of our nation’s garden centers would disagree with you), clover still has a lot to offer from a functional standpoint. We may not regularly eat shamrock salads, but clover is an important forage crop for animals we like to eat. According to the USDA, it’s “the most important pasture legume.” It’s nutritious and delicious herbivores like to eat it. As a nitrogen-fixing crop, it adds this essential nutrient back into the soil using gaseous nitrogen from the atmosphere making it useful as a cover crop in pastures and crop fields. Therefore, any traits that can be added as markers on a genetic map of this important crop are useful for breeding strategies in general. That kind of luck isn’t just frivolous, it’s practical.


*All photos were used with permission. Copyright Kristie Phillips, all rights reserved.

**All part of my larger plan for world domination.

References and Links:


One thought on “The Science of the Shamrock

  1. Pingback: Shamrock Clover Tattoo Designs – Your Lucky Charm With You Forever | Irish Clicks

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