Two years ago, I discovered that I had a kale seedling with three seed leaves, or cotyledons, rather than the usual two. I had another one show up this year.
When I was planting chard, carrots, mitsuba, beets, and lettuce in the fourth garden bed earlier this week, I discovered a “volunteer” seedling, probably red giant India mustard, that has four seed leaves.
I marked the plant with a stick and will watch how it grows. The kale seedling from 2014 that had three seed leaves grew normally.
Kale and mustard are both members of the cabbage family, as you might guess when you see how similar their seeds and cotyledons are. I wonder if plants in that family have a higher incidence of extra seed leaves. I’ve never seen excess cotyledons on my other seedlings, although I’ve read online about them showing up in non-cabbage plants.