Seeds

Autumn is the time for many plant species to spread their seeds before dying or entering dormancy for the winter.  Every seed is a potential new plant, but it is unable to move on its own.  Seeds must rely on wind or water or animals or gravity.  There are several ways that seeds leave the parent plant and move to new locations.  These methods are described below including examples of plants that you can observe on your local walks in the coming weeks.

Seeds are contained inside the fruit of plants.  The size, shape, texture and presence of special structures on both the fruit and the seed contribute to the method of travel.  Some fruits travel on their own, carrying the seeds with, but many ripen while still on their host plants, then split open and allow the seeds to travel by themselves.  Seed and fruit surfaces may contain spines, glues, fluffs or hooks that aid the seed in its travels.

Wind can move seeds a short distance or many miles depending on the air speed and direction.  Winged fruits containing one or more seeds are pulled down by gravity while being carried short distances by the wind.  A childhood favorite, the “helicopters” from maple trees, recently fell.  Others using the wind are  lightweight fruits and seeds with a cotton-like, feathery plume attached that can travel great distances on windy days.  Examples include fruits of the quaking aspen and seeds from milkweed, thistle, and dandelion.  Small, extremely light seeds may be carried on their own by even a light breeze.  Eastern prairie-fringed orchid and poppy seeds are dust-like in form, and are easily whisked away from flower heads by any air movement.

Animals, including humans, move many seeds, sometimes unknowingly and other times with a purpose.  Some species of plants have an aril, a small food treat, attached to each seed.  Insects will carry seeds back to their nests to eat the aril, but discard the seed.  Ants move hundreds of yellow dog tooth violet and Jack-in-the-pulpit seeds every autumn.  Many seeds are contained in fleshy fruit eaten by animals that later excrete the undigested seeds elsewhere.  Fruits harvested by humans are moved indoors or to local farmers markets and grocery stores.  How many of you have apples, strawberries and apricots at home?  Nuts and acorns have a leathery covering containing one or more seeds and are often cached by birds and squirrels for the winter, then forgotten and left to germinate in spring.  Many fruits are covered with barbs and hooks that attach to animal fur or human clothing as the plant is brushed against.

Many plants that grow near water, including oceans, lakes, and rivers, grow corky fruits containing air spaces that allow the fruits to float and travel with the water currents.  Sycamore and water lily are two examples.  Coconut palm originated in the South Sea Islands, but can be found growing on most tropical shorelines around the world.  One last travel method is used by explosive fruits that burst and shoot out their seeds for several feet in all directions.  Look for spotted touch-me-not, lupine and plants in the bean and pea families.

Big seeds often travel short distances and small seeds may travel far away.  Round seeds move across the uneven terrain and flat-sided seeds stay wherever they initially land.  If every seed fell beneath its parent plant, competition for resources would become fierce, and many plants would die.  It is important that seeds can move about, finding suitable locations to grow over a wide area contributing to the natural diversity of habitats.