St. Patrick’s Day is just around the corner and shamrocks abound. The problem is that people can’t agree what a shamrock is. If you research the topic you’ll find that shamrock means ‘small clover’, but when you search for shamrock images almost all show a leaf resembling wood sorrel (Oxalis) not a clover. People also argue whether it should be three leaflets or four.
This might seem trivial to most people, but to a botany enthusiast like me proper identification is important. Leaf edges of clovers are finely toothed and wood sorrels smooth edged ones. Leaflets are also roughly oval whereas those on wood sorrels are heart-shaped. Both are in separate families.
Flowers are different too. Clovers have tiny flowers in tight clusters forming ball-like inflorescences called umbels. Colors are white, pink, crimson or lilac. Hop clovers have yellow flower clusters. Wood sorrels have larger flowers with five petals that may be white, yellow or pink.
Nearly all botanists agree that the true shamrock is a clover, and most sources consider white clover to be the original shamrock. White clover (Trifollium repens) was brought here by European settlers and quickly established and naturalized throughout the continent. Native Americans called it ‘white man’s foot grass’ because the leaflets resembled toes and it was soft underfoot.
White clover is everywhere except on extremely acid soils, and it fixes its own nitrogen. It requires little or no fertilizer. White clover is genetically diverse with a plethora of natural ecotypes that adapt to different environments. All require good light and would not grow well indoors.
This is where the wood sorrels come in. Some folks insist shamrocks aren’t clovers. They even consider the heart-shaped leaves to be part of the folklore. Many species of Oxalis grow well indoors and are commonly called shamrocks. Most are either annuals or tender perennials. We have several perennial species that grow well here. They produce bulbs and are quite prolific.
Several Oxalis cultivars also have four leaflets instead of three. Many people think these four-leaf types are the true Irish shamrock, since they assume four-leaf clovers are lucky. Numerous people also attribute luck as an Irish trait and these four-leaf types fit in nicely.
According to most sources, true shamrocks have three leaflets. St. Patrick used them to symbolize the Holy Trinity. Why many symbols show four-leaf shamrocks is a mystery. Some say the fourth leaf stands for luck. Others insist it symbolizes God’s grace.
One thing’s for sure. If you find a four-leaf clover search that same plant and you’ll likely find another. It’s a mutation but the trait is genetic. You can impress your friends by finding several after encountering the first one. There’s no luck to finding them. Careful observation and patience is key.
As long as we’re exposing myths, St. Patrick couldn’t have driven the snakes from Ireland. Snakes never were native there. This was simply a metaphor for Christianity ridding Ireland of its former pagan ideology. Nobody received credit for driving snakes from New Zealand, and they have none either.

Oxalis growing in early March

White clover growing in dormant turf in mid-March

White clover plant in early spring

Ted Manzer teaches agriculture at Northeastern High School.