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, commonly called goldenrods
, is a genus of about 100 species of flowering plants in the family Asteraceae. Most are herbaceous perennial species found in the meadows and pastures, along roads, ditches and waste areas in North America. There are also a few species native to Mexico, South America, and Eurasia. Some American species have also been introduced into Europe and other parts of the world.
Solidago species are perennials growing from woody caudices or rhizomes. They have stems that can be decumbent to ascending or erect, ranging in height from 5 to 100 or more centimeters. Some species have stems that branch near the top. Some Solidago species are hairless others have strigose, strigillose, hispid, or short-villous hairs. The basal leaves in some species remain persistent through flowering, while in others the basal leaves are shed before flowering. The leaf margins are often serrate, and leaf faces may be hairless or densely hairy; the distal leaves are sometimes 3-nerved, and hairless or sparsely to densely hairy with scabrous, strigillose, or villous hairs. In some species the upper leaves are stipitate-glandular or sometimes resinous. The flowering heads usually radiate, sometimes discoid, with (1–)2 to 1500+ florets in racemiform (club-shaped or pyramidal), paniculiform or corymbo-paniculiform, or sometimes secund arrays. The involucres are campanulate to cylindric or attenuate. The ray florets are pistillate and fertile. The corollas are yellow or rarely white and are usually hairless. The disc florets are bisexual and fertile and number 2 to 35 typically, but in some species there may be up to 60 florets. The corollas of the disc florets are yellow and the tubes are shorter than the throats. The fruits are cypselae, which are narrowly obconic to cylindric in shape, they are sometimes somewhat compressed. The cypselae have 8 to 10 ribs usually and are hairless or moderately covered with stiff slender bristles. The pappi are very big with barbellate bristles.
The many goldenrod species can be difficult to distinguish, due to their similar bright, golden yellow flower heads that bloom in late summer. Goldenrod is often unfairly blamed for causing hay fever in humans. The pollen causing these allergy problems is mainly produced by Ragweed (Ambrosia sp.), blooming at the same time as the goldenrod, but is wind-pollinated. Goldenrod pollen is too heavy and sticky to be blown far from the flowers, and is thus mainly pollinated by insects. Frequent handling of goldenrod and other flowers, however, can cause allergic reactions, leading some florists to change occupation.
Solidago species are easily recognized by their golden inflorescence with hundreds of small capitula, some species have their flowers in spike-like inflorescences and others have axillary racemes. They have slender stems, usually hairless but S. canadensis shows hairs on the upper stem. They can grow to a length between 60 cm and 1.5 m. Their alternate leaves are linear to lanceolate. Their margins are usually finely to sharply serrated.
Propagation is by wind-disseminated seeds or by spreading underground rhizomes which can form colonies of vegetative clones of a single plant.
They are mostly short-day plants and bloom in late summer and early fall. Some species produce abundant nectar when moisture is plentiful, or when it is warm and sunny.
Use and cultivation
Parts of some goldenrods can be edible when cooked. Goldenrods can be used for decoration and making tea. Goldenrods are, in some places, held as a sign of good luck or good fortune. They are considered weeds by many in North America but they are prized as garden plants in Europe, where British gardeners adopted goldenrod long before Americans did as garden subjects. Goldenrod only began to gain some acceptance in American gardening (other than wildflower gardening) during the 1980s.
They have become invasive species in other parts of the world including China; and Solidago canadensis which was introduced as a garden plant in Central Europe, has become common in the wild and in Germany is considered an invasive species that displaces native vegetation from its natural habitat.
Goldenrods are attractive sources of nectar for bees, flies, wasps, and butterflies. Honey from goldenrods often is dark and strong due to admixtures of other nectars. However when there is a strong honey flow, a light (often water white), spicy-tasting monofloral honey is produced. While the bees are ripening the honey produced from goldenrods it has a rank odor and taste, but finished honey is much milder.
Goldenrod is a companion plant, playing host to some beneficial insects, and repelling some pests. They are used as a food source by the larvae of various Lepidoptera species (see list of Lepidoptera that feed on goldenrods). The invading larva induces the plant to form a bulbous tissue mass (called a gall) around it, upon which the larva then feeds. Various parasitoid wasps find these galls and lay eggs in the larvae, penetrating the bulb with their ovipositor. Woodpeckers have adapted to peck open the galls and eat the insect in the center.
Canadian Goldenrod (Solidago canadensis)
Cultivated goldenrods include: S. bicolor, S, caesia, S. canadensis, S. cutleri, S. riddellii, S. rigida, S. shortii, and S. virgaurea. A number of cultivars have been selected and a number of them are of hybrid origin. A putative hybrid with aster, known as x Solidaster is less unruly, with pale yellow flowers, equally suitable for dried arrangements. Molecular and other evidence points to Solidaster (at least cultivar Lemore) being a hybrid of Solidago ptarmicoides and Solidago canadensis (the former is now placed in Solidago, but is the "aster" of the name, as it has had a checkered taxonomic past).
Inventor Thomas Edison experimented with goldenrod to produce rubber, which it contains naturally. Edison created a fertilization and cultivation process to maximize the rubber content in each plant. His experiments produced a 12-foot-tall (3.7 m) plant that yielded as much as 12 percent rubber. The tires on the Model T given to him by his friend Henry Ford were made from goldenrod.
Extensive process development was conducted during World War II to commercialize goldenrod as a source of rubber. The rubber is only contained in the leaves, not the stems or blooms. Typical rubber content of the leaves is 7 percent. The resulting rubber is of low molecular weight, resulting in an excessively tacky compound with poor tensile properties.
Solidago virgaurea is used in a traditional kidney tonic by practitioners of herbal medicine to counter inflammation and irritation caused of bacterial infections or kidney stones. Goldenrod has also been used as part of a tincture to aid in cleansing of the kidney or bladder during a healing fast, in conjunction with potassium broth and specific juices. Native Americans chewed the leaves to relieve sore throats and chewed the roots to relieve toothaches.
The goldenrod is the state flower of the U.S. states of Kentucky (adopted March 16, 1926) and Nebraska (adopted April 4, 1895). It used to be the state flower of Alabama, being adopted as such on September 6, 1927, but was later rejected in favour of the camellia. Goldenrod was recently named the state wildflower for South Carolina.
The Sweet Goldenrod (Solidago odora) is also the state herb of Delaware as of June 24, 1996.
In Midwestern states in the mid-twentieth century it was said that when the goldenrod bloomed, it would soon be time to go back to school—the blossoms appeared in mid- to late August, shortly before the traditional start of school on the day after Labor Day.
In Sufjan Stevens' song "Casimir Pulaski Day", the narrator brings goldenrod to his girlfriend upon finding out that she has been diagnosed with bone cancer. Carrie Hamby's song "Solidago" tells the story of Thomas Edison's experiments with making goldenrod a domestic source of rubber that ended with the invention of synthetic rubber during WWII. The Blondie song Golden Rod from the album The Curse of Blondie compares the narrator to the plant as "another blonde, not from the city".