An accessory fruit is a fruit that contains tissue derived from plant parts other than the ovary. In other words, the flesh of the fruit develops not from the floral ovary, but from some adjacent tissue exterior to the carpel (for example, from receptacles or sepal). As a general rule, the accessory fruit is a combination of several floral organs, including the ovary. In contrast, true fruit forms exclusively from the ovary of the flower.[Esau, K. 1977. Anatomy of seed plants. John Wiley and Sons, New York.]
Accessory fruits are usually indehiscent, meaning that they do not split open to release seeds when they have reached maturity.
Incorporated organs
The following are examples of accessory fruits listed by the plant organ from which the accessory tissue is derived:
[Merriam Webster Collegiate Dictionary entries for syconium, accessory fruit, core, and strawberry, Merriam-Webster, Inc., 2006]
Fruit with fleshy seeds, such as pomegranate or mamoncillo, are not considered to be accessory fruits.
Examples
Apples and pears
The part of apples and pears that is consumed is, in fact, the
hypanthium. The ovary is the papery core that surrounds the apple seeds. As the hypanthium ripens it forms the edible tissues.
Roses
For roses, the hypanthium is the tissue that composes the edible part of
Rose hip. Roses and apples are both members of the Rosaceae family; the fact that they have similar fruit morphology is a major consideration in placing them in the same taxonomic family.
Strawberries
The edible part of the
strawberry is formed, as part of the ripening process, from the receptacle of the strawberry flower. The true fruits (hence, containing the seeds) are the roughly 200 pips (which are, technically,
, a true fruit that contains a single seed from a single ovary). These pips dot the exterior of the strawberry.
Cashew apple
The
cashew apple is an oval- or pear-shaped structure that develops from the pedicel and the receptacle of the cashew flower and is technically called a
hypocarpium.
It ripens into a yellow or red structure about long.
The true fruit of the cashew tree is a kidney–shaped
drupe that grows at the end of the cashew apple; the seed inside this drupe is the cashew nut of commerce.
Pineapple
The pineapple is formed when 50 to 200 unpollinated flowers coalesce in a spiral arrangement— the flowers form individually and then fuse as a single '
multiple fruit'. The ovaries develop into berries and the fruit forms around an intercalary spike. The intercalary
inflorescence (cluster of flowers) results when the terminal cluster of flowers are left behind by the growth of the main axis of the plant. Each polygonal area on the pineapple's surface is an individual flower.
Research
Current research has proposed that a single class of
may be responsible for regulating accessory fruit formation and ripening.
A study using strawberries concluded that hormone signaling pathways involving
gibberellic acid and
auxin affect gene expression, and contribute to the initiation of accessory fruit development.
Metabolic modifications in different developing accessory fruit tissues are due to the varied distributions of compounds such as
triterpenoids and
.
See also
