Ryokugyu appears to have eaten a Devil Fruit of an unknown type that enables him to generate various plant life from his body at will and freely control it. The plants he creates can be grown rapidly and moved around freely, seemingly not being limited by any rigidity that some plants, such as trees, normally possess.
Ryokugyu can generate large quantities of plants to unleash overwhelming large-scale attacks; when attacking the Beasts Pirates, he turned his fingers into sharpened tree branches and freely grew them to impale dozens of enemies over a large area with ease.
Additionally, Ryokugyu’s plants can rapidly absorb any liquid they touch, which includes dehydrating living creatures after impaling them, leaving them as shriveled husks. He appears to be able to taste the liquid he absorbs, as shown when he impaled a barrel of alcohol with a branch and remarked on its flavor.
Ryokugyu can also perform highly unorthodox feats with the plants he generates, such as growing a giant flower on his back and using it to fly by spinning it rapidly like a propeller.
It has also been shown that ordinary grass, trees and flowers grow in his wake, on any surface Ryokugyu touches, resulting in him leaving behind a trail of plants wherever he walks.
This was shown when Udon, which is known to be a barren and desolate area was shown with greenery for the first time in many years. It is currently unknown if this is passively active or something he does on purpose.
Despite having not eaten in three years, Ryokugyu has remained completely healthy and not lacking in energy. This can be made possible thanks to his devil fruit, since he has been shown absorbing liquid into his body via his plant-based Devil Fruit, with water being a key source of nutrients for plants.