The Sunflower Hill Chronicles, Part 13: The Time of Seeds
By Birgitta Jansen
August 4, 2022
As I wander up Sunflower Hill, the promise of fall is no longer just a promise. The glow of that lush and intense green of spring lasted into the summer, but now it’s a memory rapidly fading. Instead there is a stiff westerly breeze moving the grasses in waves. The interplay between light and wind transforms the hillside into a sea of sun-bleached yellow in constant undulating motion. The colorful abundance of flowers is no more. Here and there are still a few harebells, their blue a surprise. I see some nodding onion and a few diminished-looking yarrow flowers, the last reminders of summer. I look for the sagebrush mariposa lily along the Sunflower Hill Trail. They are late bloomers and I found them on The Hill not long ago. Now there’s not a trace left of their existence. But although the plants are drying, they are fulfilling their destiny: replenishing the seed bank so their species may come to life next spring.
I thought I had learned a little about flowers and plants. But now I couldn’t even tell which flowers produced which seeds. Okay, lesson learned. Next spring I shall pay more attention to the shapes of the leaves. Still, this time of seeds leaves us much to ponder.
Seeds are amazing. When we get them in a package in the store, they may not look too amazing because they are dormant, but don’t be fooled by their quiescence. They are viable and alive! Given the right conditions of water, oxygen, temperature and light, they can grow into tiny plants or huge trees and everything in between. They can grow into wild flowers, ornamental shrubs, or food crops.
Dormancy is actually a very important phase in the life of many seeds. Seeds have to be able to patiently wait until conditions are right for germination to occur. That is critical for the plant’s survival. Seeds of the same plant might even remain dormant for different lengths of time so that the seeds don’t all germinate at once. They are hedging their bets, so to speak, because conditions might turn out to be right for one batch but not the other, and so on. And the right conditions for germination also differ greatly for different species, as well as from ecosystem to ecosystem.
There are many facts about seeds that leave one to consider seeds with wonder rather than take them for granted, or perhaps not think about them at all. Did you ever question how seeds know to grow upwards instead of any which way in the soil? To be honest, I never even questioned it because it is so much the way it is and has always been. But I recently learned that plants sense gravity. The root (radicle) grows down towards gravity, while the shoot (plumule) grows upward to emerge from the soil and come into the light. The tender little shoot evidently senses light and grows towards it, just like a potted plant placed right next to a window always reaches for the light. On my kitchen counter is an onion lying on its side that has started to grow. The onion must have been stored upright because the little shoot was initially pointed straight up. But when I put it down on its side, the shoot was now positioned sideways. Soon enough, I noted that the onion would have none of that and almost within a few days, the now-several green shoots started to make a 90-degree turn to go straight up again. I can only marvel at it. An onion that senses what’s up, down or sideways?!
What most seeds have in common is that they contain all that is necessary for a new plant to grow and survive: an embryo, an endosperm and an outer seed coat that protects the seed. The endosperm surrounds the embryo and provides it with the nutrients it needs when it first begins to sprout. The endosperm also plays a significant role providing food for humans and other animals, such as wheat, corn and rice. The seed coat varies greatly. Some are thick (think coconut), and others are more easily breached.
The earliest land plants that evolved 468 million years ago reproduced using spores. Spores do not have a food source, whereas seeds have all they need to get started packed within them (the endosperm). Spores need to land in favorable conditions where nutrients are readily available, whereas seeds can afford to wait if they need to. Non-flowering plants like mosses, fungi and liverworts produce spores, and we can find those well represented on Sunflower Hill. It is astonishing to contemplate that mosses, algae, lichen and fungi have been around for millions of years. Ferns are also among the earlier spore-bearing land plants, but Sunflower Hill is too dry for them.
To consider the many different kinds of seeds that exist, we need to dive into a bit of a rabbit hole. To start with, there are the naked seeds (gymnosperms) and the enclosed seeds (angiosperms). Good examples of both can be found on The Hill. Naked seeds include the seeds found in the cones of coniferous trees. On Sunflower Hill, we find Douglas fir cones and Ponderosa pine cones. Squirrels and chipmunks know all about those! Enclosed seeds can usually be found in fruit, such as kinnikinnick, saskatoon and juniper berries.
Even though gymnosperms (the naked seed plants) evolved first, the angiosperms (enclosed seeds) are now the most common plants. There is also an enormous variety in the shapes and sizes of seeds. But before we make our way any deeper into this rabbit hole, I would suggest taking a stroll up Sunflower Hill to see what kinds of seeds you can find!
In order for plants to spread, the seeds need to be dispersed. It is important that they gain some distance from the parent plant, because otherwise the seedlings would start to compete with the parent for light and water. This competition may compromise the parent plant or decrease the seedling’s chances of survival.
The subjective estimate is that there are between 250,000 and 300,000 plants in the world, of which approximately 90% are seed-bearing plants. It’s perhaps needless to say that different ways of dispersal have evolved because, as already mentioned, seeds must be spread away from the original plant. The three main ways of dispersal are by water, wind or animals.
If the seeds are dispersed by water, they must be buoyant. To my knowledge, we don’t have any plants on The Hill that produce seeds that require dispersal by water. But dispersal by wind is another matter. Sunflower Hill has both Douglas pines and Douglas maple trees that have winged seeds (naked seeds) that make it easy to be carried off by wind. Orchids, such as our beloved calypso orchid, have countless tiny, almost dust-like, seeds that can also easily be dispersed by wind. And then there are the dandelions and the yellow salsify that produce very lightweight, hairy seeds. Because of their structure, these seeds can cover quite some distance when carried away on the currents of wind.
Animals are very important where it comes to seed dispersal. Some seeds have barbed, hooked, sticky or prickly seed coats that attach to animal fur or human clothing (some seeds favor socks…), and drop off later. Some seeds are eaten by animals and dispersed in scat or droppings. Other seeds are stored by squirrels, for example, and if not eaten, might find themselves in conditions optimal for growth.
As I am nearing the end of today’s walk, I think about this wondrous world of plants. I stop once more to take a closer look at all the different types of grasses that are gracefully waving in the wind surrounding the entrance of Campground Trail. I marvel at their beauty and diversity, as well as the fact that very important food crops such as wheat, corn and rice are grasses. Then a sobering thought occurs to me that all animal species, including humans, depend on plants and therefore on seeds. We can’t survive without them. But they could happily live without us, as they did for millions of years before we came along. Now that’s a startling thought…
All photos by Birgitta.