Moonflowers are weeds created by Luna Girl. It is a type of plant that needs moonlight to grow and it doesn't like any artificial light source nor the sunlight. Moonflowers also dislike water. It appears in "Owlette and the Moonflower" and "Wolfy Garden". It is unknown where moonflowers originate from.
Owlette and the Moonflower
Luna Girl plants a Moonflower seed that would sprout into a overgrown Moonflower with her Luna Beam so that when it blooms, she'll be able to turn the city into her giant weed garden. However, the Moonflowers were destroyed by the PJ Masks by using a source of light and water.
Another moonflower was then planted by Owlette. However, the moonflower is of a normal flower's size, and the PJ Masks need to protect the moonflower against the Wolfies rather than destroying it this time. It is also revealed that a moonflower has a sweet smell in this short.