Other plants as host plant for monarchs

Hello,
I'm wondering if the monarch larva can also eat leaves of other plants. I have no milkweed but have butterfly plants and in fact have found larvae on them. I recently found one viable larva and put it in a jar, with a branch and some of the plant's leaves, with the intention of getting some milkweed leaves. I also added 1 or 2 leaves of purple cone flower and beard tongue. Your thoughts?

Karen says:
Monarchs only eat milkweed. What are your "butterfly plants"? Are they butterfly weed? There are many different types of milkweed. Check out this information on milkweed plants.
I am not familiar with any butterflies that eat purple cone flower leaves or bearded tongue.