Rowan's tree-like form makes it easily missed when you go out on strolls in the forest. Rowan holds a mysterious power that can cure any ailment, but its shy disposition means it never really gets the chance to put this ability to use.
Alder is the evolved form of Rowan, and the resemblance to a tree is even more noticeable. But being an Alder is busy work, and all the movement makes it an easy Astromon to spot.
"When Arboreo sat down in an open glade to bathes its leaves in the sunlight, it suddenly found itself surrounded by tiny Astromons. Some had even climbed upon its shoulders and were nibbling its branches. But Arboreo fretted not and remained still so as not to injure the little creatures, and after a while, Arboreo extended its arm branches so the Astromons would find easier to climb. It was peace in motion, and not a scene I will be able to forget for as long as I live."
-Excerpt from "Essays on Astromon Society" by Telem the Obscure