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Seed dispersal

life science Maturity 9-11 Next article →

Seed dispersal is the movement of seeds away from a parent plant. Since plants have limited mobility, they must rely on various methods to spread their offspring. This process is vital for the survival and growth of plant populations. Dispersal helps plants reach favorable habitats and colonize new geographic regions. It also reduces competition with the adult plant for resources like light and water. Furthermore, moving away from the parent helps seeds avoid high concentrations of predators and pathogens.

Epilobium hirsutum - Seed head - Triptych
Epilobium hirsutum - Seed head - Triptych

Scientists divide seed dispersal into two main categories: autochory and allochory. Autochory occurs when a plant uses its own internal mechanisms to move its seeds. This method usually limits how far the seeds can travel. Allochory occurs when an external agent, known as a vector, transports the seeds. These vectors can be non-living, such as wind or water, or living, such as animals. Many plants actually use more than one dispersal phase to move their seeds. This sequential process is known as diplochory.

Geranium sanguineum02
Geranium sanguineum02

Autochory includes several distinct methods. One type is barochory, which uses gravity to disperse seeds. Heavier fruits, like coconuts or apples, simply fall from the plant when they are ripe. Another type is ballochory, or explosive dehiscence. In this process, seeds are forcefully ejected by internal pressure or tension. The Hura crepitans, often called the dynamite tree, is a famous example. Its fruit explosions are powerful enough to throw seeds up to 100 meters. Other plants, like witch hazel, use a non-explosive version of ballochory to squeeze seeds out at 45 km/h.

Geranium sanguineum02
Geranium sanguineum02

Wind dispersal, or anemochory, is one of the most primitive dispersal modes. Seeds may float on the breeze or flutter toward the ground. Dandelions use a feathery structure called a pappus to travel long distances. Maple trees use winged fruits called samaras to help them flutter down. Some plants, like tumbleweeds, move by letting the entire plant blow in the wind. However, wind dispersal requires the production of many seeds to ensure some land in good spots. Some species, like those in the Asteraceae family on islands, may evolve smaller dispersal capabilities over time.

Photos-photos 1088103921 Floating
Photos-photos 1088103921 Floating

Hydrochory is the process of dispersal through water. This is common for both aquatic and land-dwelling species. Many seeds are waterproof and can float for extremely long periods. For example, water lily seeds float before sinking to take root on the pond floor. Palm tree seeds can use ocean currents to travel between different continents. Mangrove trees also rely on water, as their seeds can be carried away by high tides. These seeds are ready to grow as soon as they touch soil.

Entada phaseoloides MHNT graines
Entada phaseoloides MHNT graines

Animals contribute to dispersal through a process called zoochory. This can happen via epizoochory, where seeds attach to the outside of an animal. Plants often develop hooks, spines, or sticky mucus to facilitate this. An example is the clover, which uses stiff hairs to cling to animal fur. It is estimated that fewer than 5% of plant species use this specific method. Another way is endozoochory, where animals eat fleshy fruits. The seeds then pass through the animal's gut and are deposited in droppings. This can increase the speed and success of germination.

Bur Macro BlackBg
Bur Macro BlackBg
Epizoochory - black Labrador with hooked Geum fruits in his fur
Epizoochory - black Labrador with hooked Geum fruits in his fur
071021redyellowblue (1674475840)
071021redyellowblue (1674475840)

Long-distance dispersal (LDD) is a special category of spatial dispersal. It is measured in two ways: proportional distance and actual distance. Proportional distance looks at the percentage of seeds that travel the farthest. Actual distance uses a specific threshold, such as 1 kilometer, to define LDD. There is also a non-standard form of LDD that involves unpredictable events. For instance, a tree seed might travel to a different continent by sticking to a shark's egg case. These extreme dispersal events are essential for plant fitness and migration.

Example of Epizoochory var. Anthropochory - Cenchrus spinifex burs on boot and trouser leg
Example of Epizoochory var. Anthropochory - Cenchrus spinifex burs on boot and trouser leg
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🖼️ Images & Media (10)
File:Epilobium hirsutum - Seed head - Triptych.jpg
Epilobium hirsutum - Seed head - Triptych.jpg
File:Geranium sanguineum02.jpg
Geranium sanguineum02.jpg
File:Photos-photos 1088103921 Floating.jpg
Photos-photos 1088103921 Floating.jpg
File:Entada phaseoloides MHNT graines.jpg
Entada phaseoloides MHNT graines.jpg
File:Bur Macro BlackBg.jpg
Bur Macro BlackBg.jpg
File:Epizoochory - black Labrador with hooked Geum fruits in his fur.jpg
Epizoochory - black Labrador with hooked...
File:071021redyellowblue (1674475840).jpg
071021redyellowblue (1674475840).jpg
File:Epizoochoria NRM.jpg
Epizoochoria NRM.jpg
File:Example of Epizoochory var. Anthropochory - Cenchrus spinifex burs on boot and trouser leg.jpg
Example of Epizoochory var. Anthropochory...
Human-Mediated-Dispersal-of-Seeds-by-the-A...
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