>>35007950Serperior wears a coat of plant fibre that blooms around it, acting as a photosynthetic material to warm its cold blood. Snakes often spend a lot of time in one spot, sometimes up to months, so it's completely justifiable that plants can grow around it in this wait in the same way Torterra has moss upon its spikes.
Chesnaught is quite obviously a chestnut and the line takes after the anatomy of such. Its whole body is arguably one big plant.
Decidueye wears plants as clothing in order to collect energy throughout the day whilst it sleeps as it is a nocturnal creature. While not completely natural, if Torterra passes your qualifications for its ability to host plant life upon its body then you should not have a problem with Decidueye working in a symbiotic relationship with the plant life it wears.