Seed Dispersal

How do plants, rooted to one place, ascertain a far and wide spread of their seeds?

Plants do not move, so they use everything that moves as their seed dispersal agents, be it wind, water or animals. The seeds are structurally modified for each agent to ensure efficient dispersal.

Wind borne seeds are winged or plumed like those of dandelion or milkweed. Water disseminated seeds like those of coconut, yellow eyed cerbera and pond iris, rely on buoyancy to float. Seeds spread by animals and birds are either attach to mobile agents or are ingested and later passed out without any adverse effect on their viability. Some fruits/seeds such as burdock, sandbur, and cocklebur have beards, spines, hooks or barbs that stick to the hair of animals and are carried away to different locations. Many of us have unwittingly served as the agents of a sandbur or a cockelbur while hiking. Many fruits from trees such as hazelnuts, oaks, elders etc are collected by squirrels, nuthatches, jays in winter for consumption. The seeds of leftovers or the dropped fruits may germinate in right conditions. Man, of course, is one of the most efficient dispersal agent. The practice of agriculture allows the most widespread and organized seed dissemination of cultivated plants. However, weeds are quite wily and sometime hitch hike a ride as adulterants with the crop seeds.

Then, there are the explosive spreaders; plants in which the fruits explode at maturity and shoot the seeds several feet away from the mother plant. Witch hazel can shoot out its seeds as far as 40 feet. Jewelweed or touch-me-not, okra, wild vetch, birdsfoot trefoil are all seed shooters.

With so many various methods for dispersal at their disposal one would think that plants are on top of their 'offspring dispersal' program. But where is the fun? You read the article and think 'Ok, I knew that, and so what?' Plants are using their tried and tested methods of furthering their generation and that is that. But wait! Knowing that these very methods have evolved over many, many years, in itself, is awe inspiring. But what is even more breathtaking is the fact that plants can master and evolve to survive in the most difficult conditions. Its a harsh reality that many are unable to keep up with urban sprawls taking over their habitats and are becoming rare or extinct. But there are fighters, like Crepis sancta, that evolve rapidly to survive. Crepis sancta belongs to the family Asteraceae and like other members of this family, produces both lighter, wind dispersed seeds and heavier seeds that drop on the patches near the mother plant. In urban setting, with more concrete than soil patches, the chances of germination and survival of heavier seeds that fall on the patches near the mother plant are better than the lighter, wind borne seeds that may be lost as they fall on concrete. The study conducted by French scientists also shows that compared to plants picked from countryside, the urban plants produced greater percentage of heavier seeds when grown in similar conditions in labs. Using genetic models, the scientists estimate a time period of about 12 years for the occurrence of this kind of change, which is relatively quite rapid.

This is one of the real good examples of how plants are struggling against the forces of nature and human atrocities to survive and making a real good job of it. Man may think he is the master but mother nature knows best.