aril

Distinguish from aryl, which is a type of organic chemical radical or Aril the Etruscan Atlas

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

An aril (or arillus) is any specialized outgrowth from the funiculus (attachment point of the seed) (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, such as the edible parts of the mangosteen and pomegranate fruit, the mace of the nutmeg seed, or the hairs of a cotton plant.

The aril may create a fruit-like structure (called a false-fruit). False fruit are found in numerous Angiosperm taxa. The edible flesh of the longan, lychee, ackee and Lleuque fruits are highly developed arils surrounding the seed rather than a pericarp layer. Such arils are also found in a few species of gymnosperms, notably the yews and related conifers. 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.

Aril development in Taxus

In the photographs of a European yew (Taxus baccata) 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.

See also

• Elaiosome

Picture Gallery

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

Acacia salicina pod displaying bright red arils attached to black seeds.

References

• Anderson, E. & Owens, J. N. (2003). Analysing the reproductive biology of Taxus: should it be included in Coniferales? Acta Hort. 615: 233-234.

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