Sproutling, A.K.A. Experiment 509-A, is the seedling of Sprout. Sproutlings float through space on solar wind in order to find objects to cling on to, in hopes of finding a piece of rock or other suitable environment for their roots to grow and continue on their father's legacy (i.e. his original programming).
Although Sprout reappeared in the Japanese version of the Stitch! anime, he makes no appearances in the English dub, where he was mentioned by Jumba to still live on Kauai. Instead, in both appearances, they are a seedling spawned from Sprout called a "Sproutling", codename: Experiment 509-A. A seedling first appeared in "Son of Sprout", which had attached to a meteor that later crashed onto the island. Once it got its roots into the ground, it quickly began to grow, carrying out his father's original programming, before eventually being neutralized.
Another Sproutling appears in "Sprout 2.0", where it was captured by Hämsterviel and genetically enhanced with the DNA of none other than Experiment 627, making the Sproutling super-strong. Luckily, Stitch and friends were able to stop the Sproutling by utilizing 627's weakness: laughter.
- Since the Japanese version of Stitch! was non-canon when this aired, this experiment is still just Sprout. However, the English dub attempted to fit the anime into the canon of the TV series, and so Sprout stays in Hawaii, whereas instead, both of his appearances are considered to be seedlings that he has spawned.