The tufts are normal, perhaps where a new stem will grow.

Not being able to see the flaky stuff I'm going to guess you made sure it wasn't scale. It was probably either residue from watering or some part of the stem-skin itself.

Other possibility, especially with indoor growing is powdery mildew. Very common on my overwintering herbs.

Thanks so much. The plants otherwise appeared to be completely healthy and growing rapidly. The white flakes were only on the stems. There is nothing on adjacent plants. So, not really sure then how to check for scale.

Can you submit a really good image so that we can see these flakes?

Unfortunately, I did not save these. If they recur I will do so. Thank you again for your help.