Unusual root growth.

[Kveldssanger]

Had a look at my book "Plant Galls" by Arnold Darlington - nothing in there.

[Kveldssanger]

A root nodule that has perhaps become deformed?

[JaySmith]

There's a bit in diagnosis of ill health p137 about galls. It talks about the bacterium agrobacterium tumefaciens. Says the bacteria is in the soil and enters through wounds, could be possible in this case?

[treeseer]

More like a burr aka burl. No sign of another agent at work, as in a gall. Not so unusual for meristematic tissue to grow in a bundle like that on trunks; why not roots?.

When you dig around perhaps you will see downward growing lateral roots coming off the burl.

At any rate this should be considered a positive feature until proven negative. Theories on damage and infestation may fit this case, IF evidence points in those directions.