Aril

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Distinguish from aryl, which is a type of organic chemical radical.

Mature and immature arils of Taxus baccata, a European yew. A fleshy aril surrounds each seed.

Close-up of pomegranate arils - The seed can be seen inside the translucent flesh.

An aril (or arillus) is a fleshy covering of certain seeds formed from the funiculus (attachment point of the seed).

The aril may create a fruit-like structure (called a false-fruit) and is produced by a few species of gymnosperms, notably the yews and related conifers in the families Taxaceae and Cephalotaxaceae. Instead of having a woody cone as is typical of most gymnosperms, the reproductive structure of the yew consists of a single seed that becomes surrounded by a fleshy, cup-like covering. This covering is derived from a highly modified cone scale.

In the photographs of a European yew (Taxus baccata) at right and below, note that the aril starts out as a small, green band at the base of the seed, then turns brown to red as it enlarges and surrounds the seed, eventually becoming fleshy and scarlet in color at maturity. The aril is attractive to fruit-eating birds and is non-toxic (all other parts of the yew are toxic), serving therefore to promote dispersal of the yew seed by birds, which digest the fleshy aril as a food source, and pass the seed out in their droppings.

The fleshy aril which surrounds each seed in the yew is a highly modified seed cone scale.

The term aril is not limited to yews. It means any specialized outgrowth from the funiculus (or hilum) that covers or is attached to the seed. It is sometimes applied to any appendage or thickening of the seed coat in flowering plants, an example being the edible parts of the pomegranate fruit. Another famous example is the mace of the nutmeg seed. The edible flesh of the longan, lychee, and ackee fruits is a highly developed aril surrounding the seed rather than a pericarp layer.