Q.I found this at the base of my plant. What is it?
A. This looks like crown gall. Not a big problem. It is a cancer like growth that is woody caused by a bacterium which lives in the soil, Agrobacterium tumefaciens. Note the second name resembles the word "tumor" because it produces a tumor like growth.
Just clip it out (with a sanitized pruning shears) and don't worry about it. Somehow the bacterium was transferred from the soil to the stem when it was cut. Most likely the pruning shears was laid on the soil and got dirty and was not sanitized before it was used to cut the branch.