Marlene, I have seen this before and did not notice any ill effects from it.

Quite some time ago there had been photo's shown on a FB group of a Blistering type effect on branch or caudex. There was no exact science for it's cause, but I wonder if this could be a similar issue and it is a way for the plant to release or get rid of excess of some sort.

With yours and one of mine, possibly little scars from where the layer of tissue of bark splits to reduce/eliminate sap?

Rick

Thanks Rick, I don't feel that's it's a problem. Doesn't seem to affect the growth of the plant and they all look healthy. Just a bit ugly on the stems.

Looks like layers of dead cells with suberin, a rubbery, waterproof material found in higher plants. It is also found in "cork", the outerlayer of bark. The main function of suberin is to hinder water and harmful solutes from entering the plant but, if I recall correctly, it is also part of the sealing tissue after wounding or leaf abscission.