Botany Seven - Fruit

In everyday language “fruit” is widely understood to refer to a plant produced, fleshy structure. They may be sweet, or sour, but are usually edible in a raw state. In Botany however, a fruit is defined as the “seed bearing structure of a flowering plant (an Angiosperm) that is formed from the Ovary after flowering”. Consequently, in Botany many structures such as nuts and grains among others are regarded as fruit.

Angiosperms have evolved these structures over millennia to take advantage of other animals, including Humans, need for nutrition and utilise that drive to disseminate their seeds. These symbiotic relationships may be general or may be specific between participants. Humans have for a long time selected those plants which produce the most, or the biggest, or the tastiest fruit, and they now account for a substantial portion of global agricultural output. Over this time many Fruits have acquired great cultural and symbolic significance; Apples to name one.

In Horticulture Fruits have two main uses: As nutrition, where you will see then described in terms of, timing, quantity, size and flavour: And ornamentally, where you will see them described in more botanically accurate terms relating to their type, and colour as well as the previous qualities. Whether you intend to eat them or appreciate their visual qualities fruit are a fascinating stage in the lifecycle of plants.

Culinary Vs Botanical

While I’ve heard it told that if you eat it with custard it’s a fruit, and if you eat it with gravy it’s a vegetable when it’s not on a plate this definition fails.

In Culinary language a fruit is a fleshy, sweet or sour product of a specific plant e.g., Apricots from an Apricot tree, Lemons from a Lemon tree, or Pear from a Pear tree; hard, oily, plant produce in shells are referred to as Nuts e.g., Acorns, Hazelnuts; savoury plant produce are referred to as vegetables, e.g., Courgette, Pumpkin, Tomato; and small, hard, plant products with thin walls are referred to as cereal or grain e.g., rice, wheat, corn (Maize).

Botanically, all of the above examples are Fruit.
Botanical Descriptions are based on observable physical characteristics, and function. For Fruit the definition is – “a ripened ovary or carpel that contains seeds”, and the Seed is defined as a “ripened ovule”. In addition to those above the following are all also, botanically, fruit; – Beans, Peas, Peanuts and all other Legumes; Cucumber, Squash and all other Cucurbits; Aubergine, Peppers & Tomato; All grains or Cereals.

Rhubarb, despite being eaten with custard is not a fruit, it’s a leaf stalk, a Petiole.

Development

Fruit development and the actual type and shape of the fruit are all intimately linked to the flower structure of the plant. Once a flower has been pollenated, and the Ovule within the Ovary has been fertilised it is the Ovary wall, the Pericarp, which begins to develop into the Fruit. In Berries and Drupes for example it becomes fleshy, and in Nuts it becomes a hard, dry covering.

Anatomy

There are three main anatomical modes of fruit development…

• Monocarpus or Simple Fruits, develop from single flowers with one or more (Apocarpous) separate, unfused Carpels. They may contain one or many seeds.
• Syncarpous or Aggregate Fruit develop from a single Gynoecium with two or more fused Carpels.
• Multiple Fruits develop from the fused Ovaries of many flowers i.e., an inflorescence.

Pericarp

• Epicarp

  From the Greek epi-, “upon” & -carp, “fruit” (sometimes Exocarp). This is the outermost layer of the Pericarp and forms the tough outer skin of the fruit, if there is one. In citrus fruit it is referred to as the Flavedo, the ‘Zest’ in culinary terms. This layer is mainly composed of materials such as cellulose for strength but also contains essential oils, waxes, fatty acids, pigments and enzymes. Often the withdrawal of chlorophyll from this layer during ripening reveals other pigments such as carotenoids (orange) and lycopene’s (red) that let dispersers know the fruit is ripe.

• Mesocarp

  From the Greek meso-, “middle” & -carp, “fruit”. This is the fleshy middle layer of the Pericarp and is the part most often eaten. It makes up most of the edible part of a Peach and a large part of that of a Tomato. In citrus fruit it is referred to as the Albedo or Pith and along with the Flavedo forms the “Peel” we remove before eating.

• Endocarp

  From the Greek endo-, “inside” & -carp, “fruit”. This is the innermost layer of the Pericarp. It may be thin and membranous like in citrus fruit where it is separated into segments and is the part that is eaten. It also may be thick and hard like in Peaches Cherries and other “stone” fruit; here the hardened Endocarp lying around the seed is termed the Pyrena. In “Nuts” the hardened Endocarp that we crack open to eat the seed is commonly referred to as the “shell”.

Fruit Classifications

There are a number physical structural (morphological) features upon which Fruit can be classified, and the order in which they are considered can yield tables which will appear to differ but contain the same classifications. Here we consider then in the following order: –

• The number of Carpels constituting the original Ovary, i.e. Simple, Aggregate & Multiple fruits.
• Pericarp nature, Fleshy, Fibrous, or hard.
• Dehiscence. -The splitting of ripe fruit along a built-in line of weakness to disperse seed, or not (Indehiscence).

Simple Fruits with Fleshy Pericarps

Drupe

Single seeded fruit with a thin skin (epicarp), fleshy mesocarp and hard endocarp E.G., Cherry, Olive, Peach, Plum.

Berry (Typical)

Single or Multi-seeded fruits with a rind or skin like epicarp covering and fleshy mesocarp and endocarp. E.g., (Single seeded) – Date, Nutmeg; One carpel many seeds – Baneberry, Barberry, Mahonia; (More than one carpel, many seeds) – Grape, Gooseberry, Potato, Tomato.

Pepo (Berry)

Multi-seeded fruits with a tough to hard, inseparable rind. E.g., Cucumber, Squash., Watermelon.

Hesperidium (Berry)

Multi-seeded fruits with a leathery separable rind comprising the Flavedo (Epicarp) and Albedo (Mesocarp). E.g., Grapefruit, Lemon, Orange.

Pome

Multi seeded accessory fruit formed from the floral tube of a compound inferior ovary. E.g., Apple, Pear, Quince, Rosehip.

Simple Fruits with Dry Indehiscent Pericarps

Schizocarp

Formed from a compound Ovary, fragments at maturity into several single seeded mericarps. E.g., Carrots, Dill, Geraniums, Mallows, Maple, Mint family (Lamiaceae).

Nut

Single seeded, formed from two or more carpels, separable hard or stony covering over a large embryo. E.g., Acorn, Beechnut, Chestnut, Hazelnut.

Tryma (Fibrous or Dry Drupe)

Some Drupes have fibrous rather than fleshy pericarps. E.g., Coconut, Pecan, Pistachio, Walnut.

Peanut

Non-typical Legume, does not dehisce.

Loment

Non-typical Legume, fragments transversely into single seeded mericarps. E.g., Sensitive Plant (Mimosa).

Achene

Single seeded, formed from a single carpel, separable covering. Also commonly seen in aggregate fruits E.g., Buckwheat, Lettuce, Sunflower.

Cypsela

Achene-like but from an inferior compound ovary. E.g., Asteraceae & Compositae families.

Samara

A winged form of Achene. E.g., Ash, Birch, Elm.

Utricle

Fruit with a thin bladder-like Pericarp. E.g., Beets, Rumex sp.

Caryopsis (Grain)

Single seeded, formed from a single carpel, thin inseparable covering that is fused with the seed coat. E.g., Corn, Barley, Oats, Rye, Wheat.

Multiple Fruits

Developed from multiple flowers of an inflorescence. E.g., Dogwood, Fig, Mulberry, Pineapple.

Seedless Fruit

Parthenocarpy is the natural or artificially induced development of a Fruit without fertilisation of ovaries taking place. This makes the Fruit seedless. In Stenospermocarpy seeds are initiated but development is aborted while the seeds are very small. Both occur occasionally in nature, but if it affects all flowers the plant is unable to reproduce unless vegetatively. Some plants have evolved to use the ability to develop seedless fruit to their advantage. In seasons where pollination is poor it can help maintain populations of seed dispersing animals. It can also act as decoy fruit to reduce predation on viable seed.

In Commercial Horticulture seed-lessness can be a desirable trait. With some crops it is difficult to ensure full pollination and hence fruit development (Figs, Tomato, Courgette); with others they would contain hard, unpalatable seed if fertilised (Banana, Pineapple, Grapes, Citrus).

Parthenocarpy in commercial horticulture is achieved by several methods. Naturally occurring parthenocarpic cultivars may be selected and propagated vegetatively, this is known to have been done with Figs from at least 6,500 years ago and quite possibly as far back as 11,200 years ago. Plant growth hormones sprayed on flowers can initiate Artificial Parthenocarpy, this is not now used as much as it was. Cultivars may be intentionally bred to be genetically triploid, (Three sets of genes). Triploids such as a Bramley Apple are self-sterile and require two compatible pollenating varieties to set viable seed. If pollenated by only one variety Stenospermocarpy results. Some parthenocarpic cultivars have been developed as Genetically Modified Organisms.

In the veg plot at Crosby Holme Grown we prefer to let plants and pollinators interact as nature intended.

Botany Eight – (coming next!!!)→

Further Resources

Most of the main search engines will give you a result if you are looking for the meaning of a particular botanical word. If you wish to explore the subject in more detail here are a few website links to give you a starting point.

• Wikipedia – Fruit.
• Wikipedia – Fruit anatomy.
• Wikipedia – Glossary of botanical terms.
• Encyclopedia.com  – Online Encyclopedia – Botany- Fruit.
• Encyclopedia.com  – Online Encyclopedia – Plants – fruits.