Goldenrod takes the blame for hay fever that ragweed actually causes
Goldenrod blooms bright yellow in late summer, right when noses start running, so it gets blamed. The real culprit is usually ragweed, flowering at the same time and scattering light pollen on the wind. Goldenrod pollen is heavy and sticky, carried by insects, and North American pollinators depend on the plant more than on almost any other.
Solidago is a genus of roughly 100 to 120 perennial species in the daisy family, about 80 of them in North America, with a few in South America and Eurasia. Plants range from a couple of centimetres to 2.5 metres tall and spread both by wind-borne seeds and by underground rhizomes that can build a whole colony of clones from one plant. Most are short-day plants, flowering as nights lengthen in late summer and early autumn, and their golden heads look so alike that species are hard to tell apart.
Ecologists count goldenrod as a keystone plant, and some rank it first among all North American plants for supporting pollinator variety. Up to 104 species of butterflies and moths raise caterpillars on it, and 42 bee species feed on nothing else. Some caterpillars bore into stems and provoke a swollen gall to feed inside; parasitoid wasps drill into the galls to lay eggs, and woodpeckers peck them open for the insects within. When nectar flows strongly, bees make a pale, spicy honey from it.
All goldenrods share a base chromosome number of nine, but species come in many ploidy levels, from two sets up to fourteen. Those differences follow geography: in the Solidago gigantea complex, plants in the east of the continent carry four chromosome sets, while those in Washington and Oregon carry six. Botanists have long argued over neighbouring genera; Euthamia was lumped with Solidago until the 1980s, when its leaf anatomy and flowers argued for separation.
Outside its native range goldenrod has turned invasive in China, Japan, Europe and Africa. Canada goldenrod, brought to Central Europe as a garden flower, now crowds out native plants in Germany and Norway. Young leaves are edible, some Native American peoples have eaten the seeds, and florists who handle it constantly can develop allergies severe enough to change careers.
Source: Solidago
