Odd stem on coleus
Hello, I was potting some of my plants to bring in to winter over and noticed this very strange growth pattern on one of the coleus. The stems have flattened out instead of being round. It appears that this occurs when the stem has leaned over and rooted in the soil and then continued to grow.
Howard County Maryland
What you are noticing is fasciation, a growth disorder not completely understood on plants. There may be several reasons why this occurs; such as the mutation of a single cell that eventually changes the shape of the flower from round to crescent, phytoplasmas, genetics, bacterial infections, insects, etc.
See the attached link for more information https://www.uaex.edu/yard-garden/resource-library/plant-week/fasciated-2-22-08.aspx