Nature Notes: Going to Seed

A single sunflower, yellow on the outside and dark in the middle, is actually a composite of 50 to 100 flowers

   Fall is coming down the tracks and the asters and goldenrods are taking over the countryside. The two are part of the sunflower family, formerly the compositae, now the Asteraceae. The East End of Long Island is rich in aster and goldenrod species, having more than 20 local species combined. In the world of flowering plants, the sunflower family is the most ubiquitous in species, and one of the reasons for that is the way the different members disperse their seeds.
    The common sunflower or common dandelion represents the family well. A single sunflower, yellow on the outside and dark in the middle, is actually a composite of 50 to 100 flowers. The yellow petals around the perimeter are parts of the ray flowers — one yellow petal, or ray, for each floret. The center is made up of disc flowers, each of which produces a seed. The dandelion is a miniature sunflower, but is constructed similarly. We might just as well call sunflowers and other members of the family “superflowers.”
    The common sunflower that is so popular at the local garden stands is one of the few members of the family that produces large edible seeds. Of course, to get at the meat, one must break through the test, just as one needs to husk the peanut from the peanut hull in order to eat it. Birds such as chickadees, blue jays, nuthatches, and the like use their beaks and grasping feet to get to the goodies. Humans prefer to buy and eat sunflower seeds already loosed from their shells. In carrying away seeds from the sunflower disc to store or eat perched on a limb, birds drop some along the way. Whether stored or dropped, several such seeds go uneaten and germinate a good distance from the sunflower parent. Such means of spreading one’s kin is not that efficient and, perhaps, why the common sunflower and others in the genus, Helianthus, are few and far apart compared to other members of the family which have seeds that are dispersed by wind.
    Asters and goldenrod seeds have a little feathery appendage called a pappus. These pappuses can be in the form of a little parachute, not unlike the feathery appendages of milkweeds, which are not at all closely related to the sunflowers. Such little parachutes like those on the thistles, for example, can waft in a gentle breeze for miles and miles. Since most of these feathery seeds become ripe and are released in the fall when southwesterlies and westerlies prevail, seeds from western Long Island and even from west of New York City can make it all the way to Montauk. It may take several generations or only one to get there from 100 miles away or more. Over the very long haul, the movement of storms from the west, with their attendant westerlies, may account for the relatively greater number of asters and goldenrods here than there.
    Cottonwood trees also produce seeds with “sails,” but their seeds are released in the spring. Maple tree seeds come in pairs, attached to each other in a “samara” with a paravane on each side, when they drop from, say, 50 feet up, the samaras spin like the rotors of helicopters and the seeds motor away from the parent. Ashes and lindens also produce seeds with wings, one to a seed, which helps them disperse their kind well beyond their trunks.
    Not so with the oaks, hickories, and walnuts. Like apples, they don’t fall far from the tree, which would be a very poor means of dispersal if it weren’t for squirrels, chipmunks, blue jays, and other mammals and birds that harvest the nuts and store them in caches or singly to get them through the winter. A lot of these nuts don’t get eaten and germinate come the following spring. The acorn may not fall far from the tree, but it can be picked up and stored a great distance from the tree. This kind of passive dispersal works better for oaks than for hickories and walnuts, as there are many more oak species in North America than walnut species.
    The Rosaceae is one of the largest families after the Asteraceae. It contains the roses, raspberries, strawberries, crabapples, beach plums, cherries, pears, hawthorns, and many other fruit-bearing trees. The fruits the rose family species produce are pulpy and mostly edible, but the seeds in the center are practically indigestible. Just as we stole apples and carried them far away to eat them as kids, spitting out the seeds as we did, the birds and mammals that eat the fruit, defecate the seeds in a myriad of places. Seeds that pass through a digestive track germinate faster than seeds that don’t. Black cherries, also known as wild cherries, perhaps best demonstrate this kind of dispersal.
    One can hardly find a wood, heathland, old field, or scrubland without black cherries. Their seeds get around!
    The Ericaceae, or heaths, such as huckleberries, blueberries, cranberries, and so on follow closely on the heels of the Rosaceae in terms of edible fruit and dispersal of seeds by birds and mammals. Like the fruit in the rose family, most of these ripen in the late summer or fall, are deposited thereafter, and germinate in the spring. Hollies, catbriars, privets, junipers, and many other trees, shrubs, or groundcover plants don’t have nearly as many species, but their fruits are more persistent than those of members of the rose and heath families. They are still clinging to their perches in the middle of winter while the more tasty ones are long gone and serve as food for over-wintering birds and non-hibernating mammals, such as mockingbirds, house finches, wild turkeys, deer mice, squirrels, and foxes.
    It is not by chance that flowering and seed-producing plants evolved in great numbers at about the same time the birds and mammals — the last vertebrates to evolve — were expanding their numbers of species halfway through the Cretaceous period, 80 million years ago. The higher plants and higher animals co-evolved. One fed the other and vice-versa. After all, you are what you eat, and not all of what you eat remains in your body.