Not so Lucky for Science
The four-leaf clover is a universal symbol of good luck . . . unless you are a plant geneticist. For geneticists, the four-leaf clover is an inscrutable mystery that has largely eluded explanation.
White clover (Trifolium repens) is a herbaceous plant in the bean family. Though it was originally native to Europe, nowadays it can be found worldwide serving as a forage crop or ornamental ground cover. As its genus name suggests, Trifolium usually has three leaves per stem, but it is capable of producing more leaves, from the iconic four to a whopping 56.
Understanding how Trifolium produces its lucky fourth leaf is a real challenge for scientists, because the clover’s genetic structure is messier than a frat house lawn after St. Pattie’s Day. Chromosomally speaking, clover is an allotetraploid. What does that mean? Most organisms, from humans to cabbages are diploid, meaning that they possess two copies of every chromosome, one from mom and one from dad. For example, humans have 23 pairs of chromosomes, 46 in total.
White Clover is a hybrid of two different diploid species existing simultaneously in a single plant. Yes, that is confusing. This means it has four copies of every chromosome, each set belonging to a different species. To complicate matters, white clover does not self fertilize, so every time it makes seeds, those progeny represent the genetic diversity of four individual plants all mushed together. This makes it almost impossible to determine which gene was inherited from where.
Despite all this, scientists have had a little luck. Researchers have identified recessive genes that influence leaf number. These genes are also strongly influenced by temperature, with warmer temperatures encouraging more lucky clovers. Still, the exact genetic controls to form a four-leaf clover remain a tangled-up mess capable of making any geneticist howl like a banshee.
Works Cited:
Jennifer, Mach. "Looking Over Allopolyploid Clover." The Plant Cell 31 (2019): 1421-1422.
“Most leaves on a clover.” Guinness World Records, 10 May 2009, https://www.guinnessworldrecords.com/world-records/most-leaves-on-a-clover, 27 February 2021.
Tashiro, Rebecca M., et al. "Leaf trait coloration in white clover and molecular mapping of the red midrib and leaflet number traits." Crop Science 50.4 (2010): 1260-1268.
Brian Rutter, PhD, is the cofounder of Thing in a Pot Productions and a postdoctoral researcher in plant biology at Indiana University. Subscribe to our newsletter to receive our “Things About Things – Odd Facts About Plants” and video production tips in your inbox every month!