Fall 1998

[TEXT ARCHIVE WEB-PUBLISHED MARCH 2002.
ORIGINAL PRINT PUBLICATION DATE: FALL 1998.]

Thinking Like a Seed

By Robyn Flake

Returning home from a walk in the Swiss woods half a century ago, George de Mestral found his clothes and his dog's coat covered with burs. While yanking out the clinging seed capsules, de Mestral grew curious. He popped one under a microscope and discovered the hook-like structures that, after much experimentation, he mimicked in a synthetic fabric. George de Mestral invented Velcro.

Seeds are local miracles: plants as perfect, curled embryos along with their food supply, snug in protective coats, equipped with imaginative transport. They are also internally programmed. The embryos of most temperate-zone seeds stay deathly dormant — sometimes for years — until environmental signals break the spell. Seeds of the weedy mullein, for instance, won't grow in a crowd. They bide their time in the soil until the spot is shaken up by some misfortune, then grab the prime real estate before anyone else can.

The apple doesn't fall far from the tree, but where does the neighborhood raccoon then drop it? Seeds and fruits are forever taking advantage of wind, water, and the outsides and insides of animals.

Wind. The seeds of dandelions, milkweed, cottonwoods, and blazingstars have "parachutes" to facilitate air travel. Maple and ash trees produce samaras (alias helicopters), single-winged fruits structured to twirl on descent and keep the seed briefly aloft. Hop hornbeams and others have seeds surrounded by thin membranes that aid gliding. Some wind-dispersed seeds are simply light and aerodynamic, like those of many grasses; some are small almost to the vanishing point. Orchid seeds could be mistaken for dust.

Water. Many plants of wet habitats, such as marsh marigold and loosestrife, have seeds with corky coats that keep them on top of the water for weeks or months. Sedge seeds frequently have waxy coats and seedpods with air pockets that lend buoyancy.

Animals. George de Mestral, his dog, and you share this at least: you all disperse seeds. Fruit and seed adaptations for clinging to fur or cloth are vexingly common. Walk through a woodland or prairie in early fall and spend your evening stripping off tick trefoil pods. If you don't want to participate, smooth clothes are recommended.

Animals carry seeds more deliberately, too. Birds are renowned for their fruit and seed consumption, squirrels for their acorn habits. Even some reptiles have a taste for fruit and seeds. Countless seeds perish on this alimentary journey but others come out the other end in good shape. They can be even the better for it, gaining in germination potential. Buckthorn berries act as laxatives, speeding their seeds' trip through the digestive tract and limiting damage.

Humans transport valued seeds intact, planting them where desired. Other animals might cache seeds and then not return for them. Or they might eat only a portion of the seed, leaving enough for germination. Ants are notorious for this. "They carry off the seeds of spring flora like trout lily and trillium and eat the 'ant candy'," says Susanne Masi, research associate at the Chicago Botanic Garden, referring to a fat-rich attachment to the seed. Thus do ants incidentally plant the rest.

The time has come. When you walk the woods and grasslands, tune in to the miracle of seeds.

Designer Genes

Let's say you have some seed of native species and a perfect place to restore these plants. Let's say you know what it takes for the seeds to germinate and grow. Are you ready to begin?

Not so fast, some experts say. You have the right species, but do you have the right genes? The genes within seeds determine the limits of the adult plant's tolerance to environmental circumstances. The tolerance limits of individuals determines the resilience of populations buffeted by environmental change. The population's collective resilience is the fate of the species. Conservationists seek to preserve each species' unique system of genetic diversity, to walk the line between too much inbreeding and too much outbreeding.

Most plant species are distributed discontinuously. They grow in patches, often widely separated, and sometimes in very different habitats from one another. Over the generations, some genes will come to predominate in one population and others in the next. These genes are often the ones that give each population the chops to survive the range of weather, disease, soil conditions, and other ecological factors peculiar to its own spot. Jim Reinartz, senior scientist and resident biologist at the University of Wisconsin's Milwaukee Field Station, tells of white cedar trees growing in adjacent uplands and wetlands. "When their seeds were mixed and sown into both habitats, they germinated well only in the habitat from which they were collected," he notes.

Now and then populations experience "gene flow." Pollen from one group will fertilize a flower in another, or seed from one group will land and grow amidst the other, and the population will pass around fresh genes. But how often this happens depends on how each species manages its reproductive affairs. Some plants primarily pollinate themselves, or are most frequently pollinated by a close neighbor, as when a bee visits one flower, then carries its pollen to the nearest like flower. In contrast to insect-pollinated species, wind-dispersed pollen might fertilize either nearby or distant plants. The seeds themselves also vary in the distance they travel.

Most prairie grasses, for instance, rely on wind to arrange their trysts and usher away their offspring. For them, genes will be readily traded with neighboring populations. Plants of specialized habitats like bogs are often more circumspect and clannish, preferring to keep their pollen and offspring close. Most likely, their scattered populations will have little internal genetic variation, but each population will be genetically distinct from the one in the next town, or the next state.

Stern as parents, geneticists lecture about the consequences of plant sexual experimentation. This couple are too similar; that pair are too different; it will never work. Poor matches are doomed to gradations of sterility, stillbirth, genetic disease, awkward problem children.

Inbreeding — crosses between close relatives — is a worry for populations of gregarious plant species that, having been cornered and boxed into the modern landscape, suffer an embargo on their pollen and seed trade. Marcy De Mauro, superintendent of planning and development with the Forest Preserve District of Will County, found that the only lakeside daisies left alive in Illinois in the 1980s were so alike that they were biologically incapable of producing offspring when crossed together. Marlin Bowles, plant conservation biologist at the Morton Arboretum, discovered that Mead's milkweeds in Illinois were in a similar predicament. De Mauro and Bowles resuscitated the Illinois populations of these species by importing seeds from out of state.

Yet outbreeding — crossing plants from distant locations or different habitats — could also cause harm. Dan Gustafson, a doctoral candidate at Southern Illinois University, has conducted field and greenhouse experiments with Indian grass and big bluestem. "Plants from Kansas performed differently than plants from Illinois," he says. "The introduction of foreign genes (such as those from Kansas) could disrupt the genetic composition of Illinois populations." Aggressive, competitive non-local plants could overrun the natives and might later prove unable to handle an Illinois environmental extreme. In fact, so wary of the potential for outbreeding are some land managers that the Illinois Department of Natural Resources is currently removing 16 acres of cultivated prairie grasses in Vermilion County and replanting with natives to preserve the integrity of a nearby prairie remnant.

When plants that are adapted to contrasting environments interbreed, it is possible for their offspring to be dealt such ill-assorted genes that they are misfits in their mother's habitat, their father's habitat, or any habitat in between. "This can occur at any spatial scale," says Jim Reinartz. "One hypothetical extreme is crossing Wisconsin plants with North Carolina plants. The populations are adapted to very different seasonal rhythms, so the seeds might not know when to germinate. Another extreme could occur among plants that appear to be in the same population, but that are growing in subtly different habitats."

To navigate these hazards, some experts exuberantly recommend that you get to know a species' breeding system, population dynamics, and evolutionary lineages. Is such intimacy with all potential restoration targets possible? There are more than 2,000 plant species in the Chicago region. Unveiling all these mysteries for just one of them will get you a master's degree, at a minimum.

At Goose Lake Prairie Nature Preserve near Joliet, Dan Gustafson is tracing gene flow between Illinois big bluestem and cultivated big bluestem from Nebraska, a population growing from seeds that were planted there in the 1980s.

Kayri Havens, manager of endangered species research at the Chicago Botanic Garden, is exploring whether inbreeding might explain the low seed set that Marlin Bowles observed in small populations of the endangered eastern white-fringed orchid. She is examining whether two species of lobelia with different pollination systems — the cardinal flower pollinated by hummingbirds and the great blue lobelia pollinated by bees — show differences in the crossing distance at which harmful effects of outbreeding, if any, appear. Bowles and Havens have jointly investigated the strange case of the Pitcher's thistle. Bowles restored this federally endangered plant to Illinois Beach State Park, where it had been extirpated. He used seeds from the nearest existing sites where the plant was found, in Wisconsin and Indiana. By every measure, the plants from Indiana have fared better. Yet Havens' genetic analysis show that the Wisconsin plants are more closely related to the original Illinois Pitcher's thistle.

When creating seed-collecting policies, agencies concerned with ecological restoration must distill vats of biological knowledge, theory, and controversy. Local agencies typically stipulate that seed should come from sites as ecologically similar to the restoration site as practicable. They suggest that when plants are introduced to a site, seed should be collected from more than one appropriate source. Some also impose geographic boundaries such that seeds must be collected within a 25- or 50-mile radius of the restoration site.

Current policy cannot address all the shadings, cannot account for all the pollination and dispersal habits and aberrations, all the genetic intrigue of plants. But in Chicago Wilderness, local seed sources for most species are still abundant and various enough to support both continued research and seed collection within the ethical boundaries of present understanding.

Seed Fall

Throughout the summer seeds have developed, ripened, and been collected, each type at its own pace, until now they seem all at once to rush to the end of the season. We seed collectors are compelled, like all harvesters, to work long hours in shortening days. But the work brings pleasure, like the silken feel of stripping Indian grass seeds into our palms. Like the rasping rubbing of seed heads back and forth, back and forth, over a cleaning screen. Rapt in our own task, we might forget that others toil with us, then we glance up and right into the eyes of one another. And smile, knowing we share the delicious joy of direct skin contact with wildness past, present, and future. At the end of the day, we luxuriate in our fatigue. It is fall, time to gather together those things we cherish. Happy harvesting.