Accessory Fruits – Rose Hip, Apple, Pear, Strawberry.
A fruit is a seed-bearing structure that develops from the ovary and sometimes the surrounding tissue. The seeds are enclosed within the ovary wall. If the wall becomes succulent the fruit is classified as ‘fleshy’.
Accessory fruits are those in which some of the flesh is formed not just from the ovary but from adjacent tissue such as the hypanthium or the receptacle. Sometimes called a pseudocarp.
The hypanthium is a cup-shaped extension of the receptacle, which encloses the ovary. The receptacle is the upper part of the stem from which the flower parts arise.
The ovary contains egg cells (ovules) which, when fertilised, become seeds that sit on or within the fruit. The flowers of the Rose family always have some form of hypanthium – an extension of the receptacle which may range from cup-shaped to flat. One result of this is that the family has many different types of fruit, some dry (achenes) but most fleshy. Where the hypanthium completely surrounds the ovaries and becomes part of the fruit it is a pome as in the Apple and Pear which are accessory fruits.
The Hip, is the fruit of the Rosa genus. This photo shows the hypanthium of the Dog Rose species Rosa canina before the formation of the hip.
A mature rose hip in October
This photo shows a rose hip cut open to reveal the seeds. The hip consists of a red fleshy covering, derived from the hypanthium which encloses a number of yellow seeds (hairy achenes), each one formed from a single ovary.
Another example of an accessory fruit is the Strawberry in which achenes dot the outside of a fleshy fruit derived from the receptacle of the flower
Common Pear in May. This is an example of an accessory fruit where the ovary is embedded in the hypanthium. At maturity the hypanthium and ovary wall completely enclose the seeds and become the edible part of the pear.
This is the flower of the Wild Cherry. The ovary sits within the hypanthium but as the fruit matures, the hypanthium falls way so that the fruit consists of the ovary wall and the enclosed single seed. The ovary wall matures into the fleshy fruit wall plus an inner layer which encloses the seed to make up the cherry stone. This is not an accessory fruit, it is a drupe. Cherry, Blackthorn, Olive, Apricot, Peach and Plum fruits are drupes. They are often known as Stone fruits.