(From A Guide to Enjoying Wildflowers, by Donald and Lillian Stokes. Stokes Nature Guide Series. Little, Brown & Company. Pp. 164-71.)
In late summer to early fall, fields glow with the color of flowering goldenrods, a sea of gold reflecting the late summer sun. These masses of color give a unique character to the landscape, but they will soon give way to those other harbingers of autumn the asters.
Ambivalence might best describe people’s feelings about goldenrod. They appreciate the beauty of the flowers but they also associate them with the stuffy noses and water eyes of allergies from the pollen. In actual fact, its reputation for causing allergies is almost totally underserved. In August, only about 1 to 2 percent of the pollen in the air is from goldenrod. Most of it comes from a plant blooming at the same time but rarely noticed-ragweed. Ragweed is wind-pollinated, thus its pollen is especially adapted to be dry, light, and carried on the wind. Its flowers are not conspicuous, for they do not have to attract insects. Goldenrod is insect-pollinated; its pollen is sticky so that it will adhere to insects and its flowers are brightly colored to attract visitors.
The genus name for goldenrod, Solidago, comes from the Latin solidas and ago, meaning “to make whole.” This probably refers to the medicinal properties of some European species, especially their ability to aid in healing wounds. Maybe we can remember all this next summer when goldenrod is in bloom and instead of blaming it for allergies, enjoy it for its interest and beauty.
Wild and Garden Relatives
In the first year of growth after germination, Canada goldenrod grows just a leafy stem but usually does not flower. In the second year, it flowers and also begins its vigorous vegetative growth. About four to five rhizomes start to grow, radiating out from the base of the stem. These grow in fall, and the next spring each one produces another stem at its tip. Each year this continues to occur, creating round colonies of the plants. Each colony is actually a clone, for all of the stems are genetically the same. The plants in a given clone are usually the same height, but height may vary between clones of the same species. It is not unusual for clones to reach eight feet in diameter, and in the prairies they have been found up to thirty feet in diameter. These larger clones are estimated to be about one hundred years old. Sometimes the central plants in a clone die back and are replaced by other plants, creating what is called a fairy ring. Most clones are so dense with stems that practically no other plants can invade them.
With over a hundred species of goldenrod [note: there are 23 species found in PA plus two more closely related species of Euthamia], many cases of hybridization occur—the pollen from one species gets on the female parts of another species. Plants often evolve in ways that minimize this crossing over of pollen between species, and studies have shown that one of the ways goldenrods do this is through isolation in time or space. Species that bloom at the same time tend to live in different habitats so that there is less chance for pollen to be carried from one to the other. Species that live in the same habitat bloom at different times, so that when one species has pollen, the other is not in bloom. There are other methods by which plants achieve this same result, but this particular one may be quite common and may in fact occur with asters, as well, although this has not been thoroughly studied.
When goldenrod flowers are in bloom they produce a great deal of nectar and pollen, which in turn attract myriads of insects. Honeybees, bumblebees, and syrphid flies come to feed on the nectar. The bees, along with soldier beetles and longhorned beetles, also come to feed on the pollen. Ambush bugs lie waiting among the flowers to feed on these other insect visitors, and they are joined by crab spiders, which have similar predatory habits.
Gall insects are also attracted to goldenrods. These insects lay eggs on the plant; as a result of the feeding of the larvae, the plant grows a slight deformity—the gall—in which the insect then continues to live until it is mature. Four galls are common on goldenrods. On the stem may be found the ball gall, formed by a small fly, or the elliptical gall, formed by a moth. At the tip of Canada goldenrod, look for the flowerlike bunch gall, formed by a small fly called a midge. Finally, various blister galls may live on the leaves, looking like a black drop of India ink on the leaf surface. If you pull these apart, you can often find a light-colored larva inside, which is a species of midge. All of these galls in turn attract other insects. Some, called inquilines, live in the galls along with the gall maker; others, called parasites, feed on the gall makers. (For more information on all of these insects and galls, see A Guide to Observing Insect Lives by Donald W. Stokes.) [See also Pp. 159-163 in A Guide to Nature in Winter by the same author for a detailed description of goldenrod galls.]
Two other insects can be found feeding on the leaves. These are treehoppers (Pubilia, Membracidae), which poke into the leaves and feed on the sap, and goldenrod beetles (Trirhabda, Chrysomelidae), which eat the leaves as larvae and adults. An interesting relationship exists between these two insects and certain ants. In one study it was shown that a species of treehopper, Pubilia concave, lays its eggs on goldenrod plants that are near the mounded homes of Formica ants. The young treehoppers exude excess sap as they feed, and the ants crawl up the goldenrod and feed on this sap. The ants and treehoppers thus form a mutual relationship that benefits both: the treehoppers give the ants their excess sap, while the ants protect the treehoppers from predators.
But the ants go a step further in this case: they also protect the plant from predators. The goldenrod beetle, a yellowish beetle about a half-inch long with black stripes, is one of the main feeders on goldenrod leaves. When the ants and treehoppers are on a plant, the ants are aggressive to the goldenrod beetles and keep them off, thus keeping the leaves fresh for the treehoppers. Although this is a fascinating relationship, it doesn’t particularly help goldenrod, except that in most cases the treehoppers do less damage than the beetles.
By late summer and early fall, most goldenrod species have finished flowering and are dispersing their seeds. The stalks remain standing into winter, and the seeds are dispersed with little parachutes of filaments.
In each tiny goldenrod flowerhead there are two types of flowers: ray flowers and disk flowers. The ten to seventeen ray flowers around the edge have only female parts. Twenty or more disk flowers are in the center, and these have both male and female parts. For a basic understanding of this flower, see the Daisy Flower-watching section, for both plants are members of the Composite [now Aster] family.
Through the Seasons
Goldenrods are perennials. Canada goldenrod sends up a stalk the first year but does not produce flowers. The stalk dies back in the fall and the plant overwinters as roots. The next year a flowering stalk is produced along with rhizomes that will produce new stalks at their tips. Blooming occurs in late summer and fall and seeds are matured and dispersed in fall. Flowerstalks die in fall but remain standing through winter dispersing seeds. The plant overwinters as roots and rhizomes.