Magical, mysterious seeds
It's the time of year when gardeners begin planning their summer gardens and starting seeds indoors to get a head start on the growing season. No better time, then, to think about how amazing, enchanting, magical and mysterious seeds really are. They can be densely nutritious or fatally poisonous. Some are the size of a child's head; others are microscopic.
Some can live in a dormant state for thousands of years. They are opportunistic; they are ingenious. They can be breathtakingly beautiful or quite plain. They are nature's disposable, single-use containers.
In 2017 local garden writer and radio host Jennifer Jewell and plantsman/garden designer/photographer John Whittlesey created Seeds: Nature's Artful Engineering, a traveling exhibit of photographs, interpretive information and hands-on activities. Jewell presented a talk based on the exhibit to local Master Gardeners. The following information is a summary of her presentation.
Seed-bearing plants (spermatophytes) evolved 400 million years ago, coinciding with the receding water and increasing land masses on Earth. The vast variety of seed structures that evolved revolutionized the ability of the plant kingdom to travel to almost every corner of our globe. Diversity is key to the successful reproduction and survival of many species, and seeds have that in spades: that's why our globe is covered in plants.
Basically, seeds consist of an embryo and an endosperm, both of which are often contained within a protective coating called the testa. The endosperm feeds the embryo until it is successfully sent out into the world by one (or more) dispersal methods. If the seed ends up in a welcoming location, and conditions are good, germination can occur. When it does, the seed becomes a seedling, sending roots down into the earth and cotyledons up into the air. In a nutshell, that's the job of a seed: protect, nurture, disperse.
The wonder and beauty of seeds is legion — but part of the wonder lies in the variety of dispersal methods plants have evolved to ensure reproductive success. There is no form, color, texture, size or scent left unexploited in the bag of reproductive tricks developed by spermatocytes. The five basic dispersal strategies are wind, water, weight, wildlife and ballistics.
Every plant utilizes at least one of these methods and most employ several. The fact that each technique has advantages and disadvantages is a prime example of the tradeoffs and compromises inherent in evolution.
WIND (ANEMECHORY) >> Reliance on wind is a common method (think pine trees, rice and other grasses), but not the most efficient. This is why plants with seeds designed to be whisked away on the wind produce enormous amounts of light, aerodynamic seeds. When you depend on the vagary of air currents, you can't be choosy about where you land, and producing lots of seeds dramatically increases survival odds. The structure of the seed itself creates specific movements in the air. The samara produced by the California bigleaf maple (Acer macrophyllum) is a good example: it locomotes like a helicopter until it drops to the ground.
WATER (HYDROCHORY) >> Seeds designed to take advantage of moving water capitalize on the largest sin
gle ecosystem on our globe. As Jewell says, these plants have solved the age-old dilemma of how close to live to Mama, and the answer is “not very”! The leaves of the Indian rhubarb (Darmera peltate), a riparian plant common along our foothill streams, funnel its seeds into the water flowing beneath the plant. Taking hold in the soil away from the parent, they benefit from reduced competition for resources. Conversely, seeds dispersed in this way can forfeit the advantage of existing pollinator attractors.
WEIGHT (BAROCHORY) >> Gravity-fed dispersal is the domain of conifers and trees bearing large nuts, as well as sycamores. The sheer weight of the mature seed triggers its fall to the earth. These large seeds do not easily travel under their own resources, and either sprout under the parent, or rely on animals to move them about.
WILDLIFE (ZOOCHORY) >> A variety of strategies encourages animals to disperse seeds. Through an ingenious crafting of texture, shape, and color, the plant attracts wildlife in order to hitch a ride (epizoochory) and be dropped or scraped off later, or to be consumed by an animal (endozoochory) and then deposited along with the animal's feces in a different location. Although poisonous to humans, the seeds of poison oak (Toxicodendron diversilobum) are an important food source to overwintering wildlife and the birds which migrate along the Pacific Flyway, ensuring a wide dispersal range.
BALLISTICS (BALLOZOOCHORY) >> In what is perhaps the most impressive seeddispersal tactic, explosions forcibly propel the seed away from the parent. Triggered by a change in heat or humidity, some part of the seeds' casing will contract and expand and change shape, ejecting seeds in the process. The beloved California poppy (Eschscholzia californica) is a prime example of seeds that burst open. This summer, save some poppy seeds in a paper bag, and listen to them as they dehisce (burst open).
Of our native California plants, the largest seed is that of the buckeye (Aesculus californica) and the smallest is the microscopic seed of any of our native orchids (such as lady slipper and stream orchid). The largest seed on earth is the coconut. Seeds can remain viable for thousands of years: a viable seed from a lotus was discovered in an Egyptian tomb.
Curiously, seeds whose endosperms provide the most food to their embryos often have the shortest life span, and those which provide the least amount of food can last the longest.
The UC Master Gardeners of Butte County are part of the University of California Cooperative Extension system, serving our community in a variety of ways, including 4-H, farm advisers, and nutrition and physical activity programs. To learn more about UCCE Butte County Master Gardeners, and for help with gardening in our area, visit https://ucanr. edu/sites/bcmg/. If you have a gardening question or problem, call the hotline at 538-7201 or email mgbutte@ucanr.edu.