rumex cristatus
Fruit and Plant Dispersal
All organisms have to find new sources of nutrition. Most
animals move about almost constantly in search of new
food; if they didn't then they would soon deplete the food
within their vicinity. Even stationary organisms, such as
sponges and plants, which may have everything they
need in their immediate vicinity have to find new suitable
locations for their offspring. Dispersal, in order to
colonise new sites, sequester new resources and hence
increase population numbers is a characteristic of all
living things. Bacteria, fungi and slime moulds may
produce sporing structures, elevated above the
substrate in order to reach fast flowing currents of water
or air into which to shed their spores. In flowering plants
and conifers, the main dispersal stage is the seed. In the
flowering plant the seed is enclosed inside a fruit, the
structures of which help protect the seed and also assist
its dispersal.

Many flowering plants produce fruit that are intended to
be eaten by animals, the seeds passing through the
digestive system intact to be deposited at a site remote
from the parent plant. Such fruit are typically brightly
coloured, to make them easy to find, and the swollen
ovary wall is fleshy and packed with sugars as a food
reward for the animal. Such berries are not always meant
to be eaten by any animal, however. The bright
orange-red berries of wild arum (
Arum maculatum)
shown on the left, are eaten by birds, such as blackbirds
(and possibly rodents?) but are considerably poisonous
to humans! They contain needle-like crystals of saponin
oxalates which irritate the mouth and gut, taste acrid and
reportedly can be fatal. Do birds eat these berries with
impunity? Alternatively, do they eat a few before moving
on to avoid irritation? The latter might be a way to ensure
the berries are shared between several animals and so
dispersed to more locations. Many animals do not eat all
the berries on any given plant as they have an optimum
foraging strategy which requires them to move between
available food supplies in their range, rather than
stripping one location bare. In any case many berries
end-up falling to the ground and may not be dispersed
very far.

Dispersal by Water

Of course, a number of agents may disperse the same
fruit, but plants do tend to specialise and prefer one
particular mode. The docks (
Rumex) such as Rumex
cristatus
on the left, have a fruit enclosed by the three
persistent sepals which dry and harden and at least one
of the three sepals has a rounded protuberance of corky
tissue. This is a flotation device which aids the dispersal
of the fruit in water.
samara
Berries of wild arum, Arum maculatum.
Rumex cristatus
Enchanetr's Nightshade
Left: the hooked hairs on many fruit, such as these
tiny fruit of Enchanter's Nightshade (
Circaea lutetiana)
cling to the fur of passing animals to be carried far
from the parent plant. This is an example of dispersal
by animals.
Fruit Terminology and Types

The fruit is the mature gynoecium (collective term for the female parts or carpels) along with accessory tissues. As the fertilised egg
develops, the gynoecium becomes the sole or main component of the flower. Perianth and stamens usually whither and fall. The style dries
up, except in those species in which it functions in fruit dispersal. The ovary enlarges, but may be associated with noncarpellary tissue
(
accessory tissue) which may dominate in the mature fruit.

Parthenocarpy: fruits develop without fertilisation, e.g. may occur in citrus, pepper, pumpkin, tomato and results in the development of
seedless fruits. Seedless fruit may also develop from aborted embryos, e.g. in cherry, grape, peach.

Extracarpellary tissues: Tissues other than the carpels which may contribute to fruit formation, e.g. the receptacle in strawberry, bracts
in pineapple, the calyx (sepals) in the mulberry (
Morus) which becomes tightly pressed to the ovary wall and forms an integral part of each
drupelet, and floral tube or receptacle in fruits derived from epigynous flowers, such as the apple and pumpkin. (Epigynous: The
receptacle is the swollen end of the shoot which bears the floral appendages. Bracts are modified leaves, often small, sometimes scaly,
which subtend either an inflorescence (shoot bearing one or more flowers) or a flower itself. If a bract subtends an inflorescence, such as a
flower spike, then any bracts subtending individual flowers within the spike are often termed bracteoles or secondary bracts.
Simple fruit: formed from a single pistil (one carpel or two or more united carpels) as in the bean pod, tomato, plum.

Aggregate fruit: formed from an apocarpous gynoecium with each carpel maintaining its separate identity, e.g. raspberry, strawberry.
(Apocarpous: individual carpels not fused).

Multiple fruit: derived from an inflorescence (and hence the combined gynoecia of many flowers) e.g. mulberry, pineapple. In mulberry
(
Morus) each 'berry' is a collection of tiny drupes or drupelets. (Drupe: a fruit with soft flesh surrounding a single stone).

Accessory fruits (false or spurious fruits): any of the above fruit types which contains extracarpellary tissue, e.g. the apple is a simple
accessory fruit; strawberry an aggregate accessory fruit; mulberry a multiple accessory fruit.

If the fruit is defined to include any associated extracarpellary tissue then four fruit types encompass all fruit:

1.
Aggregate fruit: carpels not united.
2.
Unit fruit: carpels united.
3.
Free fruit: formed from a superior ovary.
4.
Cup fruit: formed from an inferior ovary embedded in a cup of noncarpellary tissue or from a superior ovary enclosed in a hypanthium.

Combining these classifications we have:

1.
Aggregate free fruit: derived from an apocarpous hypogynous flower.
2.
Unit free fruit: from a syncarpous hypogynous flower.
3.
Aggregate cup fruit: from an apocarpous perigynous flower.
4.
Unit cup fruit: from a syncarpous epigynous flower.

Fruitlet: an individual carpel in an aggregate fruit.

1. Dry Fruit

Dehiscent Fruit

Dehiscent fruit commonly contain several seeds and may develop from a single carpel (follicle, legume) and are monocarpellary or from
more than one carpel (capsule, silique). In
monocarpellary dehiscent fruit, the break may occur longitudinally through the suture joining
carpel margins, the back of the carpel or both simultaneously. In
syncarpous (unit) fruits with parietal placentation, dehiscence may occur
through the suture between two carpels or through the backs of carpels. In syncarpous fruits with axile placentation, the separation along
the lines of union (septae) of joining carpels (septicidal dehiscence) may be combined with a breaking away from the central column.
flower types
The cavities inside the carpels are the locules. Each locule contains one or more ovules attached via stalks called funiculi (singular:
funiculus). Dehiscence through the backs of carpels opens the locules (loculicidal dehiscence). Longitudinal breaks may occur in other
places. Some fruits undergo longitudinal circular dehiscence involving all carpels (circumscissile dehiscence) or through pores (poricidal
dehiscence). Many dehiscent fruit are called pods.

Legumes (many Fabaceae) – derived from a superior ovary formed from a single carpel, dehisce along the carpel margins and the
median vein. In Glycine (soybean) pods, the exocarp is the outer epidermis and hypodermis, both with thickened walls; the mesocarp is
parenchyma and the endocarp includes several layers of sclerenchyma and the inner epidermis. The cells in the hypodermis have their
long axes perpendicular to those of the sclerenchyma. Thus, when the fruit dries, the outer and inner pericarp layers shrink in different
directions, setting up stresses which open the fruit. This may be enhanced by the differing orientation of cellulose microfibrils in different
layers of sclerenchyma. The valves may separate explosively and become twisted.

In
Phaseolus (bean) pod, the parenchyma beneath the hypodermis contains chloroplasts with starch granules and encloses a network of
small vascular bundles near the sclerenchyma interconnecting the median and lateral bundles and makes some beans ‘stringy’. The inner
epidermis of Phaseolus divides to form an inner layer of non-photosynthetic parenchyma, making the green pod a useful vegetable.
In some legumes (
Pisum, Vicia faba) the inner parenchyma produces multicellular hairs that extend into the locules and are thought to
maintain optimum humidity inside the locules.

Capsule (silique) – many Brassicaceae – consists of two carpels (bicarpellary) joined margin to margin and a false partition (derived
from the marginal placentae) which divides the locule in two. The exocarp and mesocarp are thin-walled and the endocarp is
sclerenchymatic. A rib develops around the partition, along the juncture of the carpels. The carpels separate along the suture, leaving the
seeds attached to the ribbed edge or frame (replum) of the partition. E.g. shepherd’s purse (
Capsella bursa-pastoris).

Follicle: a dry monocarpellary, superior, one-chambered fruit that dehisces by one suture only. E.g. the simple follicle of madar
(
Calotropis). Most often follicles are aggregates.

Indehiscent Fruit

Usually derived from an ovary in which only one seed develops, even if more than one locule is present. The pericarp (the ovary wall
which usually develops into the fruit wall) resembles a seed coat in structure and may largely replace the seed coat (achene of
Asteraceaea) or fuse with the seed coat (caryopsis of Poaceae).

Achene (Asteraceae): develops from an inferior ovary (a cypsella). One-chambered, one-seeded fruit developing from a superior or
inferior monocarpellary ovary and with a pericarp free from the seed coat. The floral tube forms extracarpellary tissue (indistinct from the
pericarp). The seed coat (derived from one integument) has a thick-walled outer epidermis and the fruit wall is reduced to an outer
sclerified tissue and some parenchyma. E.g. the simple achenes of hogweed (
Boerhaavia); most are aggregate.

Caryopsis (grasses, monocarpellary, superior, pericarp fused with seed coat). The pericarp and remains of the seed coat from the outer
layers of the wheat caryopsis. The layers are: outer epidermis (covered by cuticle), one or more layers of parenchyma, partly resorbed
parenchyma, cross cells (elongated transverse to the grain long axis and having thick lignified walls) and remains of an inner epidermis
(lignified cells elongated parallel with the grain long axis – tube cells). The outer integument disintegrates and the inner becomes altered
and compressed – it is covered by cuticle on both sides and contains a fatty pigment. The endosperm forms 83% of the fruit and contains
starch and protein. The outermost endosperm layer is the aleurone layer which contains lipids and proteins.

Wheat bran: 14% of the grain, includes the pericarp, remnants of the nucellus and integuments, and the aleurone layer.
Wheat germ: the oily wheat embryo.
Glutens: wheat proteins that affect bread making along with glycolipids which interact with the glutens.

Zea (including maize): the outer pericarp consists of cells with thick pitted walls and is compressed. The central pericarp disintegrates. The
inner pericarp remains thin-walled and is compressed, stretched or torn. The integuments disintegrate completely A cuticle occurs
between the thick-walled nucellar epidermis and the pericarp.

Cuticular layers in the seed coat are derived from the nucellar epidermis and the integuments and are fused into one layer. In wheat, a
strand of pigmented tissue interrupts this layer and this may allow water to enter the seed (?).
Millet (Echinochloa utilis): a small gap in the cutinised seed coat occurs at the base of the caryopsis and contains two cell types – nucellar
cells and cells similar to those in the wheat pigment strand. The aleurone cells opposite these nucellar cells are transfer cells with wall
ingrowths. Similar aleurone transfer cells occur in Zea.

Cypsela: a dry, one-chambered and one-seeded fruit developing from an inferior, bicarpellary ovary with free pericarp and seed coat, e.
g. Compositae: sunflower, marigold.

Samara. A dry, indehiscent, one or two seeded fruit developing from a superior bi- or tricarpellary ovary, with one or more flattened, wing-
like outgrowths, e.g. ash. The wings develop from the pericarp and the fruit splits into fruitlets, each enclosing a seed.
Samaroids: winged fruit, but with the wings derived from dry, persistent sepals, e.g. wood-oil tree (Dipterocarpus), sal tree (Shorea) and
Hopea.

Nut. A dry, one-chambered and one-seeded fruit, developing from a superior, bi- or polycarpellary ovary, with a hard and woody pericarp.
E.g. chest-nut (Castanea), oak,  beech.

Schizocarp (Schizocarpic fruit)

A schizocarp is a composite fruit (made of a gynoecium of several carpels) which splits into individual fruitlets, each fruitlet derived from
one carpel and also called a
mericarp.

Lomentum. A dry indehiscent legume with partitions between the seeds and one seed per compartment. The fruit splits transversely into
one-seeded fruitlets, e.g. gum tree (
Acacia), sensitive plant, Indian telegraph plant (Desmo-dium gyrans).

Cremocarp. A dry, indehiscent, two-chambered fruit developing from an inferior, bicarpellary ovary. The fruit splits into indehiscent one-
seeded fruitlets, called mericarps. The mericarps remain attached to the prolonged end (carpophore) of the axis. E.g. Umbelliferae:
coriander (
Coriandrum), cumin (Cuminum), anise or fennel (Foeniculum), carrot (Daucus). E.g. the cremocarp of Carum (Apiaceae) –
derived from an inferior ovary. Pericarp and accessory tissue can not be distinguished. The mericarps separate such that the united
lateral bundles and associated tissue form a column, forked at the top.

Double Samara. Maple (Acer) – develops from a superior, bicarpellary ovary. Splits into two samaras when mature, each with one wing
and one seed.

Regma. A dry, indehiscent fruit developing from a syncarpous pistil. It splits away from the central axis into cocci, each coccus containing
one carpel and one or two seeds. The dry pericarp decays to liberate the seeds, e.g. caster (
Ricinus), Geranium.

Carcerule. A small, dry, indehiscent, four-chambered fruit developing from a superior, bicarpellary pistil and is enclosed by a persistent
calyx and splits into four nutlets, each enclosing a single seed. E.g. Labiatae.

Fleshy Fruits

Drupe (stone-fruit). A fleshy fruit with one or more chambers and one or more seeds developing from a monocarpellary or syncarpous
pistil. The pericarp consists of epicarp (skin), mesocarp (often fleshy) and the endocarp (hard and stony). E.g. mango (
Mangifera), plum
and peach (
Prunus), coconut-palm (Cocos). The fruit of Prunus originates from a single carpel in a perigynous flower. The ventral suture
between the carpel margins is often visible as an indentation in plums, peaches and nectarines. The thin exocarp consists of epidermis
and subepidermal collenchyma, the mesocarp is fleshy and the sclerenchymatous endocarp is stony.

Bacca (Berry). A many-seeded fleshy or pulpy fruit developing from a single carpel or a syncarpous pistil, e.g. tomato, gooseberry,
grapes, banana. The seeds separate from the placentae in the ripe fruit and remain free in the pulp. Date palm is a one-seeded berry.
The banana (
Musa acuminata) fruit arises from an inferior tricarpellary ovary with axile placentation. In seedless parthenocarpic bananas
the ovules degenerate and the locules are filled with starch-rich pulp originating from the pericarp and dividing walls. Very little pulp is
produced in seeded varieties as the mature seeds fill the locules. The parenchyma of banana fruit walls contains numerous vertical
vascular bundles and laticifers. Inside this zone occurs aerenchyma, and then a zone with horizontal vascular bundles that connect with
the pericarp vertical bundles and the central carpellary bundles.

In the tomato (
Lycopersicon esculentum) the berry has no rind. Wild types and cherry tomatoes have two carpels, but other cultivated
forms have a variable larger number of carpels. The fleshy tissue includes the pericarp, the partitions and the placentae (which are axile,
but fill most of the locular space). Placental tissue that invades spaces among the ovules becomes gelatinous when the fruit is mature.
Absorption of red light by phytochrome and ethylene synthesis cause the green chloroplasts to change in to red chromoplasts.

Pepo. A fleshy, pulpy many-seeded fruit which develops from an inferior, unilocular or trilocular syncarpous pistil with parietal
placentation. E.g. Cucurbitaceae (cucurbits): cucumber, melon, squash, etc. The seeds lie in the pulp, but remain attached to the
placentae. The boundary between carpellary and extracarepellary tissues is not discernible. A single-layered epidermis is covered with
cuticle and has stomata. The subepidermal consists of parenchyma or collenchyma. The subepidermal parenchyma give the fruit its colour
and may have green chloroplasts or yellow chromoplasts. Fibers and phloem strands may be present and in some there is a layer of
sclereids. Beneath this sclerenchyma is parenchyma which extends to the centre of the fruit at maturity (cucumber, water melon) or id torn
and replaced by a central cavity (
Cucurbita maxima, muskmelon). The inner epidermis of the endocarp may cover the seeds in a
membranous layer. In water melon the red colour results from pigment crystals inside chromoplasts.

Pome. An inferior bilocular or multilocular, fleshy, syncarpous fruit surrounded by the thalamus. The thalamus constitutes the fleshy,
edible part. E.g. apple, pear.

The fruit of
Pyrus (P. malus, apple; P. communis, pear), the pome, arises from an inferior ovary and the bulk of the flesh is extracarpellary.
This extracarpellary tissue is interpreted as either part of the floral tube or hypanthium or as derived from the receptacle. The ovary
consists of five carpels united to form axile placentation. The outer epidermis is covered with a thick cuticle of overlapping platelets of wax.
Stomata and trichomes occur in young fruit. The stomata are later replaced by lenticels. In “russeting” apples patches of cork develop in
the outer layers of the apple. The subepidermal tissue is compact and has thickened walls. The skin is made up of the epidermis and
subepidermis. The skin of red varieties contains anthocyanins and carotenoid-rich chromoplasts also contribute to the red colour. The
flesh is mostly parenchyma with large air spaces and contains the main bundles which give off anastomosing branches throughout the
flesh. The core consists of parenchyma enclosing the median and lateral carpellary bundles and an endodermis of sclereids lining the
locules. Each locule has two or more seeds. Clusters of sclereids in the flesh of the pear.

Hesperidium. A superior, multilocular, fleshy fruit developing from a syncarpous pistil with axile placentation. The endocarp (and
mesocarp) projects inwards to form distinct chambers and the fused epicarp and mesocarp form the rind, e.g. Citrus with about ten
carpels. In lemon the exocarp (flavedo, the yellow tissue) consists of cuticle-covered outer epidermis and compact subepidermal
parenchyma with oil glands and crystal-containing cells. The mescocarp of lemon (albedo or white tissue) consists of parenchyma with
large intercellular spaces and aerenchyma and contains a vascular network. The endocarp consists of inner epidermis and a few layers of
compact parenchyma. (Peel: exocarp and all but innermost layer of mesocarp). The endocarp produces the juice sacs (multicellular club-
shaped structures with long stalks) that fill the locules. In a mature juice sac a cuticularised epidermis encloses large vacuolated cells
containing juice. Photosynthetic parenmchyma gives the exocarp of unripe fruit its green colour. These chloroplasts become chromoplasts
in the ripe fruit (the Valencia orange is orange in winter and turns green again in spring).

Balausta. Inferior, many-chambered and many-seeded fruit developing from a syncarpous pistil with usually two whorls of basal carpels
within the receptacle, forming two layers of chambers. The pericarp is tough and leathery and the chambers are made of thin-walled
carpels, e.g. pomegranate (
Punica granatum).

Aggregate Fruits

An aggregate of simple fruits borne on a single flower is called an etaerio.
Etaerio of follicles, with two or more follicles, e.g. madar (
Calotropis) and periwinkle (Vinca).
Etaerio of achenes. E.g.
Clematis, Rannunculus, strawberry, rose, lotus.
Etaerio of drupes. E.g. raspberry (
Rubus) with small drupes (drupels or drupelets) aggregated together in a fleshy thalamus. Each
drupelet has a stony endocarp of various layers of differently oriented elongated sclereids and the succulent pulp is the parenchymatous
mesocarp. The exocarp bears epidermal hairs that hold the drupelets together at maturity.
Etaerio of berries. Berries embedded in the fleshy thalamus, e.g. custard-apple (
Annona squamosa) or with distinct and separate berries,
e.g.
Polyatlhia, Artabotrys.

Multiple or Composite Fruits (infructescence)

A composite fruit develops from an inflorescence.

Sorosis. A multiple fruit developing from a spike or spadix. The flowers fuse together by their succulent sepals and the axis grows fleshy
or woody and the whole inflorescence forms into a compact mass, e.g. pineapple. Mulberry is a sorosis with the fleshy part made of loosely
attached sepals.

Syconus. Develops from a hollow, pear-shaped, fleshy receptacle which encloses a number of minute male and female flowers. The
fleshy receptacle encloses a number of achenes, e.g.
Ficus (e.g. fig, banyan).
Placentation
Achene
Seeds and Fruits Dispersed by Water

The fibrous coat of the coconut is a flotation device that
carries the coconuts across the sea. In the double
coconut (coc de mer,
Lodoicea maldivica) the fruit
weighs 18 kg and may be up to a metre in length and
takes 6-10 years to ripen. In lotus, the spongy thalamus,
bearing fruits and its hemispheric top, floats in water.
The seeds of water lily are small and light and also have
an aril enclosing air and so they can float on water.

Seeds Dispersed by Explosive Fruits

Explosive dispersal scatters seeds a few yards from the
parent plant, e.g. balsam (
Impatiens), wood-sorrel
(
Oxalis). Some seeds of the explosive fruits of
Acanthaceaea are provided with
jaculators (curved
hooks) that suddenly straighten and help seed ejection.

The fruits may burst open in either dry or wet conditions,
depending on species. Camel’s foot climber (
Bauhinia
vahlii
) has long explosive pods sometimes exceeding 30
cm in length.
Seeds and Fruits Dispersed by Animals

Hooked fruits. Hooks, bristles, spines, barbs, stiff hairs etc. allow the fruit to adhere to fur and clothes.

Sticky fruits. These have sticky glands, e.g. Plumbago, mistletoe (Viscum).

Fleshy fruits and edible fruits. Animals eat the fruit and seeds pass out with their faeces, e.g. guava, grape, fig,
dates, plums. Squirrels may disperse acorns and hazelnuts when they bury them for a winter store which they later
forget about or do not need.
Rumex obtusifolius fruit with accessory
structures (petals) and with petals
removed to show the inner nut.
The winged samara of Acer platanoides (Norway maple)
Dog's Mercury fruit
Mercuralis perennis and the Ant

Left: the characteristic double fruit of Mercurialis perennis (Dog's
Mercury) consisting of a two-seeded capsule.

These structures are rich in lipids and proteins. Dispersal occurs
in two phases. Initially dispersal is by twisting of the fruit wall as it
dries, forcefully expelling the two seeds contained within. This can
effect dispersal up to about 1 metre or so from the parent plant.
Each seed has a fleshy white appendage called an
elaiosome.
The elaiosome is rich in lipids and proteins. On average each
seed only lies about for about 25 minutes before being collected
by an ant and carried back to its nest. Seeds retrieved from ant's
nests have the elaiosome removed, suggesting that the ants eat
this. The seed is then left to germinate. This second phase of
dispersion extends the range of dispersal to several metres and
may provide optimum conditions for seed germination.
Article updated:

23 May 2015
12 Dec 2015
06 Aug 2016
Dog's Mercury seed
Left: a seed of Mercuralis perennis removed
from the fruit above. Note the white oleiosome
at the top. The brown disc at the lower right is
the placenta scar.
Rumex
Seeds and Fruits Dispersed by Wind

Wings. E.g. maple and sycamore (Acer), elm (Ulmus) and birch (Betula).

Parachute mechanism. In many Compositae, the calyx forms a pappus of hairs. The pappus opens out in an
umbrella-like manner when the fruit detaches from the parent plant. E.g. cotton.

Censer mechanism. The seeds are discharged from a dehisced fruit when the fruit is shaken by the wind. E.g.
poppy (
Papaver), loofah (Luffa).

Hairs. The seeds of madar (Caloptropis), milkweed (Asclepias) and cotton have hairs either in one or two tufts or
all over the seed.

Persistent styles. In Clematis the styles persist and are very feathery.

Light seeds and fruits. Orchids have the smallest seeds. Millions of dust-like seeds are produced in a capsule.
The fruits of some grasses are also very light.
Rumex
Above: From the shape of the fruit in the
photograph and the location (a roadside /
hedgebank near to a wood) I would say this is
Rumex sanguineus, the Wood Dock.

Right: Wood Dock growing in a beech, ash and
hornbeam, wood on calcareous soil.
From the shape of the fruit, and the single curled leaf
visible in the photo and its habitat (bordering a
meadow in Kent UK) I would say this is
Rumex crispus,
the Curled Dock.
Myosotis
Above: the hooked fruit of some Myosotis
(forget-me-not) species also catch on animal hair and
clothing.
Dogs Mercury
Above: Dogs Mercury, Mercuris perennis, is a common plant of
the woodland floor on basic or calcareous soils, such as this
chalkland beech and ash wood.
Lotus fruit
Pea-flowers (family Fabaceae) such as this Lotus (Bird's-foot Trefoil) have
characteristic pods whose valves twist when the pod dehisces and splits open,
scattering the seed.
Wood Dock
Agrimony fruit
Left: the hooked fruit of Agrimony (Agrimonia
eupatoria
).