Thanks for the question.

There is no worry; there is nothing you should do; your cup plant is quite healthy. What you are observing on the leaves are called galls. They have small mite larvae within them. With cup plants, these galls often appear as bumps or protrusions on the surfaces of leaves and stems. In trying to research your question, there are few reports of scale insects being found on cup plants (Silphium perfoliatum). That is why I am leaning towards these being galls and not scale.

The most common insect involved in galls on cup plants is something termed a gall midge (Asteromyia carbonifera). They are also seen on different species of golden rod. Both cup plants and golden rod are in the same botanical family. These galls are generally seen on leaf surfaces. Here is some information about them as well as insect galls in genera:

https://www.jungledragon.com/image/61908/gall_midge_-_asteromyia_carbonifera.html

https://extension.umn.edu/yard-and-garden-insects/insect-and-mite-galls

https://extension.okstate.edu/fact-sheets/plant-galls-caused-by-insects-and-mites.html

Here’s the deal. Last year (2023), adults of these mites were present on your cup plant. However since they were so small, it is doubtful that you ever noticed them. Here is what they look like:

https://bugguide.net/node/view/742770

These adults mated, laid eggs, and larvae emerged that burrowed into the leaf tissue. The leaves responded by enclosing the larvae with a form of leaf cancerous growth (a gall). A type of defensive response by the plant. You may or may not have seen these galls in 2023. This spring (2024), adults emerged from these galls, mated with one another, and laid eggs on the emerging leaves of your plant. Larvae quickly hatched to form the galls that you are now seeing. The whole process is repeating itself.

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