Seed dispersal
Flowering plants use various strategies to spread their seeds
Species that survive are species that reproduce and spread. Plants can't walk, so in order to spread, flowering plants need ways to get their seeds to new locations.
They use a number of different strategies that we can observe just by strolling through a field in summer, fall, or winter.
Many plants use wind or water to carry their seeds, which are attached to fine, fluffy fibers that act as parachutes. Milkweed and thistle are among the plants whose seeds fly through the air. Trees such as willow, cottonwood, and sycamore, which grow along streams or creeks, drop many of their seeds into the water, where the fluff keeps them afloat on the current so it can carry them to new spots.
Hitchhikers have miniscule hooks attached to the seed capsule so that they can grab onto the fur of passing animals or the clothes of people, to be scratched or pulled off later. Burdock burrs, in fact, were the inspiration for the invention of Velcro.
Then there are the leapers, seeds that bounce or jump away from the parent plant. Jewelweed and witch hazel have seed cases that are so constructed that when they dry out, the slightest touch causes the case to burst and project the mature seeds through the air. Black walnuts have spongy hulls so that they bounce when they hit the ground and roll away from the tree.
What we think of as fruits are actually seeds surrounded by sweet pulp that animals like to eat. Animals often take their food to a safer location to feed, and the pit is discarded after the animal consumes the pulp. If the seeds are small, they are swallowed whole and then excreted, usually far from the parent plant. Many acorns buried by squirrels are never retrieved. These acorns eventually sprout, and some grow into trees.
Species that are able to compete easily with other plants often do not have elaborate dispersal strategies but simply bear their seeds in cases that drop the seeds nearby when brushed by animals or wind. Garlic mustard, for instance, may form large, dense stands of plants. Other species don’t bother much with seeds but spread through rhizomes, or underground stems, such as wild ginger and day lily. Runners are an aboveground variation seen in strawberries.
The abundance of a species depends on many factors, but its dispersal method is often key to survival. In winter, plant skeletons offer evidence of seed dispersal.
