The Science of Botanical Art

Fleshy Fruits

By Dick Rauh

Originally appeared in The Botanical Artist, Number 31

 

Remember I left you off last time probably hopelessly confused about compound fruits. These are fruits that come from many ovaries, which group together to form a single entity. Sometimes the many separate (apocarpous) ovaries were in a single flower, like a raspberry and the resulting fruit is an aggregate. Sometimes the compound fruit comes from many flowers (in an inflorescence) like a pineapple and it is a multiple. Simple, aggregate, or multiple fruit can either be ‘fleshy’ or ‘dry’, depending on what has happened to the pericarp in its journey to maturity, and what we are going to focus on here are the various forms of fleshy fruits. The ovary wall is the predecessor of the fruit wall, and is divided into three layers, the endocarp, closest to the seed, the mesocarp in the middle and the exocarp to the outside, and often we differentiate fruit types by what happens to these layers. When the endocarp becomes hard or bony enclosing a single seed we have a drupe. These are the so-called stone fruits, all in the rose family, that make up an important economic grouping. Cherries, peaches, plums, apricots and almonds belong here, and these are truly the idea of sweet fruit that makes our mouth water. Beware of the easily opened pit, and resist the temptation to suck on the seed, because these seeds are equipped with a bit of cyanide to discourage predation. They are all from hypogynous flowers (with superior ovaries) and you can check this (and show it in your drawings) when you can see the remains of the calyx attached to the stem. The minimal scar at the opposite side of the fruit is the place where the style was attached. 

Another fruit type formed from a superior ovary, but one where the pericarp is succulent, and not differentiated into separate layers is the berry. A grape is an example, as are the fruits of the nightshades, tomatoes, peppers, and eggplants. Now we are dealing with succulent entities that are no longer sweet, that we would classify unbotanically as vegetables. It’s also true the botanical term ‘berry’ doesn’t include any of our common berries. Confusing? 

Blueberries and gooseberries for example, are classed as false berries because, although they are from fleshy and undifferentiated pericarps, they are from inferior ovaries. Note the persistent calyx is on the opposite end from the stalk attachment. Bananas are also classed as false berries, the large scar from the flower appearing on the opposite end from the branch indicating an inferior ovary. Digression here. The banana tree is not a true tree, but a large herb, and in order to produce edible fruit for the market it is essential that the flowers of the huge and monoecious inflorescences of the banana never get fertilized. To insure the continuity of the species, asexual reproduction is used. In effect the flowering branch is cut down after the mature but unfertilized fruit is harvested, and new growth from the same root system is encouraged. 

Another type of fleshy fruits from inferior ovaries is the fruit of Cucurbitaceae or gourd family, called the pepo, which has a leathery epidermis and a rind. Squash, melons and cucumbers belong here. Another fruit derived from an inferior ovary is the pome, where the endocarp has become papery (the core) surrounding the seeds. Here again the fruit is from the rose family, and logically belongs in the fruit section of the supermarket. Apples, pears, quinces are in this group, and are also known botanically as accessory fruits, because the fleshy content is derived only partially from the ovary wall. Cut an apple across and it is evident that we have a five carpellate ovary here, and a papery endocarp. What is more subtle is the ring made by vascular bundles which separates the fleshy unit contributed by the mesocarp and the exocarp (inside) and the fleshy unit contributed by the “floral tube”, stamen, petal, sepal and receptacle tissue (outside). The skin, like most of the skins on our fruits derives from the epidermis. 

The other main fruit type is a berry with the formidable sounding name of hesperidium. This is the citrus fruit of Rutaceae (note how often a fruit type is closely tied to a particular family). Here we have a fruit from a superior ovary, but this time it comes from and retains a septate ovary with axile placentation, and a thick, leathery skin with essential oils, with much of the pericarp forming ‘juice hairs’. Lemons, oranges, grapefruit are examples, and again look at how the calyx remnant clings to the stem end of the fruit and the tiny opposite scar is from the lost style. 

There are a couple of succulent compound fruits that I need to mention before closing, because in most cases the ‘fleshy’ parts are not derived from the ovaries at all. Strawberries are my favorite, because that wonderful red stuff that we love is entirely made from receptacle tissue. The ‘fruits’ of the strawberry are a kind of simple dry fruit that dot the outside of the succulent receptacle. Those aren’t just seeds, they are seeds enclosed in a hard pericarp called an achene. This is true of the rose hip, too. Here it is the fleshy (and highly vitamin C rich) receptacle, which grows around the dry fruits inside. 

A fig is a multiple where the receptacle tissue also encloses the many achenes in a delectable morsel that never had anything to do with an ovary. 

We have touched lightly on one kind of dry fruit - the achene. Next time we’ll look at a whole range of dry, but fascinating solutions to the seed dispersal problem.  

 

“Le Calville Blanc,” Pierre-Joseph Redouté, an example of ‘pome’

  • “Le Calville Blanc,” Pierre-Joseph Redouté, an example of ‘pome’