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What is this mystery plant?

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 By John Nelson

My hometown, Columbia, S.C., was discovered and originally inhabited by a group of brave Irish explorers, who, after a perilous oceanic crossing, sailed up the mighty Santee River until it got so rocky that they had to disembark on the banks of the Congaree River. There they lived and prospered, establishing a ceremonial portion of town called Five Points, and there they began a tradition of celebrating the life and exploits of their beloved St. Patrick.

On St. Patrick’s Day, great quantities of good food and strong drink were had, and much merriment occurred. This tradition has occurred up until now, when the present-day residents of Columbia swarm out of their homes, dressed all in green and wearing shamrocks, and, laughing and singing, march toward Five Points down Devine Street. OK, I’m being silly.

St. Patrick’s Day is a good time to consider the identity of the Irish “shamrock.” There has been, in fact, considerable controversy as to the correct identity of this plant. Two entirely different kinds of plants, genera actually, are involved. The reasons that these two genera are involved in this controversy is that both have very similar leaves, and more specifically, leaves with three leaflets, and that both genera occur as native species in Ireland, and would have been around at the time the legend of St. Patrick began.

The genus Oxalis consists of several species, all of which have star-shaped flowers with five petals. These plants are commonly called “sorrels.” Different sorrel species usually form clump-like growths, and if chewed, will have a sharp, sour taste. A lot of sorrels are weedy, and there are some very attractive ones that are cultivated. At least one of these has deep purple leaves, and is sold as a shamrock, but the true shamrock is not a species of Oxalis. Rather, it is a species in the genus Trifolium, a low-growing member of the bean family.

There are many species of Trifolium, and they, too, bear leaves with three leaflets. The common name for the different species in this genus is “clover.” And yes, this is where the term “four-leaf clover” comes in. Every now and then, with clovers, which typically grow not so much in clumps, but in spreading patches, you’ll find some growth anomalies that have led to 4 leaflets being produced. The same thing can occasionally happen with sorrel. Clover flowers are smaller than those of sorrels, and their shape is quite different –– not so much star-shaped as “sweet-pea” flower-shaped. Clovers don’t have that sour taste, either.

Maybe it doesn’t make too much difference if your shamrock is actually a sorrel. After all, St. Patrick’s Day is more commonly a day of welcoming spring and having fun, rather than discoursing on botanical systematics. But there is one thing you should realize: There is no such thing as a “four-leaf clover.” Those four (or three) little green things are leaflets, or divisions of a single compound leaf. So sing along with me: “I’m looking over a four-leaflet clover…”

 

[Answer: “Shamrock,” Trifolium repens]

 

John Nelson is curator of the A.C. Moore Herbarium at the University of South Carolina in the Department of Biological Sciences in Columbia, S.C. As a public service, the herbarium offers free plant identifications. For more information, go to www.herbarium.org or call (803) 777-8196 or email nelson@sc.edu.