Autumn―the season of vivid color, cooler temperatures and harvesting! It’s the end of the growing season―time to gather the last vegetables from the home garden, pick the ripened fruit from the orchard and harvest the final crops from the farm fields.
Although we’re more likely to think about seeds in the spring, it’s worth taking a moment to consider what happens to seeds at this time of the year.
Shown below a dragonfly sits on the ripe seeds of a coneflower.
A seed is “the embryonic stage of the plant life cycle” according to the Merriam-Webster dictionary. But I prefer this description― “Seeds are small plants, wrapped up in a package with the things they need to get a good start in life.”―from the Minnesota Department of Natural Resources (DNR). Of course, those small plants typically don’t start their independent lives until the spring when conditions are favorable for germination and growth.
When you stop to think about it, by autumn most seeds have matured to the stage they’re ready to leave the parent plant and travel to a home of their own. “Unlike animals, plants are limited in their ability to seek out favorable conditions for life and growth.” … “Seeds come in a great variety of shapes and sizes, and a lot of the variation relates to dispersal mechanisms.” report authors Lawrence Kelly and Cecilia Zumajo in their article What is a Seed?
Interestingly, seed-making plants can be divided into two groups: gymnosperms and angiosperms. Gymnosperms form seeds between the scales of a cone or in the berrylike cap. If you look carefully, you can see seeds on the scales of the pine cone pictured below. These seeds are often called “naked seeds” because they are easily visible. Conifers and other cone-bearing trees fall into this category.
Angiosperms, on the other hand, form seeds in ovaries which grow into fleshy fruit or nuts. The seeds are not visible as they are enclosed in the fruit or nuts.
“Every seed has a protective coat, some stored food, and an embryo that is the beginning of a new plant.” reports the Minnesota DNR in their article From Small Seeds Grow Big Dreams. “Most seed-making plants pack energy into seeds from starch, sugar, and fat.”
As a result, many animals (birds, mammals, reptiles and fish) eat seeds and the surrounding fruit, berries or nuts. The violet-colored berries of the American Beautyberry (Callicarpa americana) shrub in our yard, are a case in point. These berries are popular with many birds including mockingbirds and warblers.
The seeds of a magnolia tree are also distinctive. Cone-like structures called “aggregates” develop from the magnolia blossoms. Each aggregate contains multiple seeds. In the fall, as the seeds ripen, they turn a bright red attracting birds and other wildlife.
Unknowingly, birds and animals ingest the seeds of the fruit, berries or nuts they consume. Eventually, these seeds end up in a new place along with the animal droppings. “Endozoochory, in which animals consume seeds or fruits that are then passed in their feces, is of major importance as a means of dispersal.” says the Encyclopaedia Britannica.
From a botanical perspective, fruits are the mature ripened ovaries of flowers and all fruits enclose and protect seeds. Thus, many of the items we think of as vegetables are actually fruits. Bell peppers, tomatoes, cucumbers, eggplants, and green beans are examples.
In addition, to being transported by ingestion, some animals collect and stash nuts. It’s common to see squirrels, for instance, gathering and hiding acorns during the fall. They eat most of the nuts during the winter but some are forgotten and left to grow.
“Epizoochory”, which is the dispersal of seeds by attaching to the outside of animals, is another way in which animals disperse seeds. The seeds involved in this process, called burs, have tiny barbs and hooks which attach themselves to an animal’s hair or fur to hitch a ride.
Another dispersal mechanism, called “anemochory”, is distribution by the wind. Plants which disperse their seeds this way have seeds which are adapted to be caught and carried by the wind. The common dandelion is a case in point. Who hasn’t blown on a dandelion seed head to make all those fluffy little parachutes float through the air?
Milkweed, cottonwood, asters and cattails also rely on anemochory to distribute their seeds. Shown below is the seed pod from the Anglepod Milkvine, a member of the milkweed family which is native to the southeastern USA. Initially, the seeds are hidden inside a pod but when the pod bursts open, dozens of tiny seeds with fluffy, parachutes spring out.
A maple tree is another example of an anemochore. Its winged seeds, known as “samaras”, are often likened to helicopters or propellers as they whirl their way to the ground.
“Hydrophily” is seed dispersal by water. Lotus plants, which grow in water-covered mud, use this method. The flower of the lotus is strikingly beautiful and highly regarded in Chinese custom where it is considered a symbol of purity. When the lotus bloom becomes a pod, it dries and drops seeds onto the water’s surface. The water’s current carries the lotus seeds to new locations. Eventually, the seeds will land in mud along the bottom of a pond, or similar body of water, and new lotus plants will emerge.
Another method of seed dispersal is through simple gravity referred to as “barochory”. Many trees and plants merely drop their seeds and let them fall to the ground. Grains, such as rice, corn and cereal grains, are technically seeds fused to the ovary wall of the fruit. The slender stiff bristles that grow from the flower of wheat, barley, rye and other grasses are called “awns”.
Interestingly, scientists studied the awns of wheat to better understand how the wheat plant disperses its seeds. In the 2007 issue of Science journal, they reported “the dispersal unit of wild wheat bears two pronounced awns that balance the unit as it falls. … the awns are also able to propel the seeds on and into the ground. … The energy source for this active movement is the daily cycle of air humidity.”
Apples and other tree-grown fruits are also dispersed by barochory. As the fruits grow and get heavier, gravity causes the branches to bend and, eventually, the ripened apple falls to the ground where it may settle or roll to a new location. It’s true the apple doesn’t fall far from the tree!
Of course, humans also disperse seeds. In my previous blog post, 79,000 Steps and a Whole Lot of Apple Seeds, I shared a story about the abundance of wild apples along the Island Walk in Prince Edward Island. Much of the trail, which follows previous railway lines, was unexpectedly bordered with wild apple trees. An interpretive sign along the trail explained why: “At one time every farm had an orchard or at least a couple of trees of different varieties. By the mid-1800s, apples were a part of the rural culture. They were stored for the winter in cold rooms, or dried or preserved like valuables. … They were an obvious choice also for lunch baskets taken on the reliable but sometimes slow trips by train. Cores went out the window. It would seem that both rail workers and passengers are the most likely culprits responsible for the proliferation of apple” trees along the trail.
As you can see, seed dispersal is an important aspect of nature. “Plants and trees need water, light, and nutrients to survive, but these resources are limited. By spreading seeds further afield, plants will be able to make the most of available resources without having to compete.” explains author Karen Bradshaw in her March 2024 online article, Plant Delivery Systems: Understanding Seed Dispersal. “In order to ensure the survival of any given species, the more widespread it can be, the better. On top of this, having the ability to spread seeds over greater distances means greater biodiversity in any given area. These things combined mean that the plant species will be able to thrive and survive.”
More Info
Previous blog posts mentioned in today’s blog post include:
. 79,000 Steps and a Whole Lot of Apple Seeds about my experience walking the Island Walk on Prince Edward Island.
The following articles were consulted in the writing of this blog post:
. From Small Seeds Grow Big Dreams article by Minnesota Department of Natural Resources (DNR)
. Plant Delivery Systems: Understanding Seed Dispersal article by Karen Bradshaw.
. The Role of Wheat Awns in the Seed Dispersal Unit by Rivka Elbaum et al. Science journal article May 2007.
. What is a Seed? by Lawrence Kelly & Cecilia Zumajo, New York Botanical Garden article Apr 2021.
Today’s Takeaways
1. “Seeds are small plants, wrapped up in a package with the things they need to get a good start in life.” Minnesota Department of Natural Resources
2. “Seeds come in a great variety of shapes and sizes, and a lot of the variation relates to dispersal mechanisms.” Lawrence Kelly and Cecilia Zumajo
3. Seed dispersal is an important aspect of nature.
