The term aril, in botany, means the external part of the seed that grows together with this. Aril is usually fleshy and colorful.
This semen envelope, which can be total or partial, originates from a hyperplasia of the ovular funiculus.
When the seed matures, the aril often takes on a lively color, which favors its endozoocora dissemination in which the plants with fleshy fruits (berries or drupes) are appetite by birds or mammals and whose seeds are then dispersed through the feces.
On some seeds (euonymus etc.) there is an outgrowth called arylodine (or aryloid or false aril), Due to an enlargement of the integument in correspondence to the micropilar rim. It can extend over the whole surface of the seed; if small it is called caruncola (as in castor and in other Euphorbiaceae).
In other cases, as in the badger, this produces poisonous seeds surrounded by an edible red aril, which is the only part of the plant harmless to humans and pets.