For some time ago I noticed that most of my bananas had small black spots on them. I don't think this is because of spider mites because in that case the leaves get more bronze/bright yellow stripes and you can actually see the mites crawling around. Here are some pics:
That is my basjoo on which you can see small black dots.
Also this california gold has it.
This SDC has most dots on its pseudostem.
This is an older leaf of a ensete ventricosum and as you can see it's almost turning black underneath but none of the others have this much under the leaf. All of the plants have spots on the surface, more or less.
What could this be?