In botany, a diaspore is a plant dispersal unit consisting of a seed or spore plus any additional tissues that assist dispersal. Examples of such additional structures includes elaiosomes, fruits, pseudofruits or arils, as well as pappi. In a few plants, the diaspore is a tumbleweed and comprises most of the plant.
Diaspores are common in weedy and ruderal species. Collectively, diaspores, seeds, and spores that have been modified for migration are known as disseminules.
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A dispersal vector is an agent of biological dispersal that moves a dispersal unit, or organism, away from its birth population to another location or population in which the individual will reproduce. These dispersal units can range from pollen to seeds to fungi to entire organisms.
There are two types of dispersal vector, those that are active and those that are passive. Active dispersal involves pollen, seeds and fungal spores that are capable of movement under their own energy. Passive dispersal involves those that rely on the kinetic energy of the environment to move. In plants, some dispersal units have tissue that assists with dispersal and are called diaspores. Some types of dispersal are self-driven (autochory), such as using gravity (barochory), and does not rely on external agents. Other types of dispersal are due to external agents, which can be other organisms, such as animals (zoochory), or non-living vectors, such as the wind (anemochory) or water (hydrochory).
Geocarpy is "an extremely rare means of plant reproduction", in which plants produce diaspores within the soil. This may occur with subterranean flowers (protogeocarpy), or from aerial flowers, parts of which penetrate the soil after flowering (hysterocarpy). It has evolved as an effective means of ensuring a suitable environment for the plant's offspring.
Geocarpy is also linked with solifluction soils, where rapid thawing and freezing of surface soil causes almost continuous movement. This phenomenon is prevalent in high altitude areas of East Africa. In order to reproduce, geocarpic plants bend their stems so that the fruit can be embedded in the soil during the freezing process while the fruit is still attached to the plant itself.
Drift seeds (also sea beans) and drift fruit are seeds and fruit adapted for long-distance dispersal by water. Most are produced by tropical trees, and they can be found on distant beaches after drifting thousands of kilometres through ocean currents. This method of propagation has helped many species of plant such as the coconut colonize and establish themselves on previously barren islands. Consequently, drift seeds and fruits are of interest to scientists who study these currents.
In botanical terminology, a drift fruit is a kind of diaspore, and drift seeds and fruits are disseminules.