Wind Dispersal

In Spermatophyte plants, seed dispersal refers to the movement, spread or transport of seeds away from the parent plant. Plants show limited mobility and are dependent upon a variety of dispersal vectors in order to transport their seeds, this involves both the abiotic vectors, like those of the wind, and biotic (living) vectors like those of birds. Seeds are able to get dispersed away from the parent plant individually or in groups, it gets dispersed in both space and time. Patterns of seed dispersal can be easily determined in large quantities with the help of the dispersal mechanism and this plays a crucial role in the demographic and genetic structure of plant populations, along with the migration patterns and species interactions. There are five major modes of seed dispersal such as gravity, wind, ballistic, water, and also by animals. Some plants are only able to disperse their seeds in response to an environmental stimulus. These modes are basically the results based on adaptations, like those of wings or fleshy fruit. Although, this simplified view ignores the complexity in dispersal. Plants possess the ability to disperse in modes without having the typical associated adaptations and plant traits might be multifunctional.

Types Of Wind Dispersal

Wind dispersal of seeds is further divided into five types each form is discussed below:

Gliders

The entire seed possesses a wingspan of about 5 inches (i.e. 13 cm) and thus the seed is capable of gliding through the air of the rainforest in the form of wide circles. This seed has inspired the design of early aircraft and gliders. Gliders comprises seeds having two lateral wings that look similar to the wings of an airplane. They are airborne when released from their fruit and sail through the air similar to a true glider. One of the common examples of this method is Alsomitra macrocarpa, a tropical vine of the Gourd Family (Cucurbitaceae) is native to the Sunda Islands of the Malay Archipelago.

Parachutes 

This comprises seeds or achenes (one-seeded fruits) having an elevated, umbrella-like crown of intricately-branched hairs at the top, mainly produced in globose heads or puff-like clusters. The slight flow of wind attaches with the extended crown of plumose hairs, raising and propelling the seed into the air similar to a parachute. This method is the classic mechanism of dispersal for the Eurasian dandelion (Taraxacum officinale) and comprises a number of weeds and native members of the Sunflower Family (Asteraceae). A giant Eurasian form of the dandelion known as the salsify or goat’s beard (Tragopogon dubius), is presently one of the most successful wind-travelers of North America.

Helicopters (Whirlybirds)

Helicopters (also referred to as Whirlybirds) comprises seeds or one-seeded fruits (samaras) possessing a rigid or membranous wing at one end. The wing mainly possesses a slight pitch (similar to a propeller or fan blade), resulting in the seed to spin whenever it falls. Based on the velocity of the wind and distance above the ground, helicopter seeds can be carried away to considerable distances away from the parent plant. The spinning action is the same as auto-rotation in helicopters, as the helicopter “slowly” comes down due to a power loss.

Flutterer/Spinners

They are the native range of hopseed bush (Dodonaea viscosa), and belong to the member of the Soapberry Family (Sapindaceae), which is situated from Arizona to South America. It is also usually cultivated in southern California. They are papery, winged fruits that flutter and spin in the air, and can be carried to short distances via the wind.

Cottony Seeds & Fruits

These are fuzzy brown having cattail spikes (Typha latifolia) composed of dense masses of tiny seeds, each possessing a tuft of silky hairs. Each spike comprises approximately a million seeds. They are shed down by the millions in a cloud of white fluff. Cottony seeds and fruits involve seeds and various minute seed capsules having a tuft (coma) of cottony hairs at one end, or seeds attached in a cottony mass. For  example this group is somewhat similar in function to that of the parachute seeds, but generally they are not carried far by the wind.

What is fruit dispersal?

Fruits play a vital role in the seed dispersal of a variety of plant species. In dehiscent fruits, like those of poppy capsules, the seeds are generally dispersed directly from the fruits that remain on the plant. In fleshy or indehiscent fruits, the seeds and fruits usually move away from the parent plant together. Plants like grasses and lettuce have the outer integument and the ovary walls completely fused, so that the seed and fruit form one entity; these types of seeds and fruits can be referred together as “dispersal units,” or diaspores.  

Conclusion

We can easily observe wind dispersal by blowing a dandelion. Seeds from plants such as dandelions, swan plants and cottonwood trees are light and possess feathery bristles and can be further carried to long distances by the wind. Some plants, such as kauri and maple trees, are composed of  ‘winged’ seeds. These do not float away but only flutter to the ground. With wind dispersal, the seeds are mainly blown about and land in all kinds of places. To increase their chances that at least a few of the seeds land in a place that is suitable for growth, these plants must  produce lots of seeds.