A stalk of goldenrod colonizes a roadside planting in the Longwood Hospital area in Boston.
Ragweed by cottonmanifesto. A sidewalk crack near the same location.
Urban species #223: Goldenrod Solidago canadensis
Urban species #224: Ragweed Ambrosia artemisiifolia
Ragweed and goldenrod are often discussed together. These two plants, both common in urban, suburban and countryside contexts, bloom at around the same time toward the end of the summer. Goldenrod (any of more than a hundred species commonly found in North America) produces showy plumes or crowns of tiny yellow flowers. Often it colonizes a field or lot and turns the whole area into a bright wash of color. When I was growing up, any time anyone sneezed in late summer, some parent blamed the goldenrod. The ubiquitous weed was an obvious scapegoat--doubtless that all that yellow must be producing huge amounts of irritating pollen. Of course, the goldenrod's color is intended to attract insects to mechanically transport the pollen from one place to another, and relatively little goldenrod pollen should be drifting on the air (though it can cause human, and canine, allergy suffering). Instead we can blame those plants with flowers with no attractants for insects--no strong odor or bright color. We can point to many kinds of grasses, and then those weeds with green flowers: mugwort, lambsquarters, and of course, ragweed.
Ragweed is considered the worst allergy-producing pollen. Along with its pollen's virulence, we also must cope with the plant's abundance. Ragweed grows well in the city, in poor soil compacted by foot traffic. It's seeds are high-quality food for birds, notably seed-eating urban species such as rock pigeons and house sparrows, who will spread the plant far and wide.
Native Americans used a tea of ragweed roots to alleviate menstrual pain, and rubbed ragweed on their skin to treat insect bites. As ragweed is known to cause contact dermatitis, one can speculate on its affect on skin already irritated by a mosquito bite. The pollen of at least one species of ragweed (Giant ragweed A. trifida) is harvested to make anti-allergy medication.
Goldenrod also has a history of human association. Reportedly it was used to help heal wounds (resulting in the Genus name: Solidago, to make whole or solid) by the Crusaders. Also, when folks in Boston were angry about a certain tax on imported tea, they made "liberty tea" from goldenrod. I'm frankly skeptical about this last use, as goldenrod is one of the only plants uneaten in the deer enclosure that I maintain at work--and those deer eat poison ivy and garlic mustard. In addition to tea, apparently the blossoms can be fried, like dandelion flowers are, into fritters.
Along with the insects that pollenate them, there are many species of insects that use goldenrod as a kind of nursery. There are spittle bugs, hiding in protective froth attached to the stems, and then there are several kinds of insects that inhabit the stalks themselves, causing the growth of goldenrod galls. Some birds, such as downy woodpeckers and black-capped chickadees are attracted to goldenrod fields, in order to feed on the larvae inside their galls.
This ragweed growing in a flowerpot outside of North Station in Boston demonstrates the plant's ability to spread and appear in unexpected places. Photo by urbpan.
Goldenrod by cottonmanifesto. Location: Parkway Road, Brookline. A rare single stalk, of a plant that forms thick stands. (This, and remaining photos by cottonmanifesto.)
A close-up of ragweed, showing the stalk on which the flowers, and then the fruit, appear.
A close-up showing the many tiny flowers that make up the goldenrod blossom.
This sidewalk tree planting in Brookline is entirely surrounded by ragweed.