Type of FlowersGoldenrods:
Goldenrods,called Solidago, is a genus of about 100 to 120 species of flowering plants in the aster family, Asteraceae. Most are herbaceous perennial species found in the meadows, pastures, and waste areas of North America. Also, a few species are 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. Their stems can be decumbent to ascending or erect, ranging in height from 5 to 100 or more cm. 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 serrated, and leaf faces may be hairless or densely hairy; the distal leaves are sometimes three-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, or are 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 two 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 cylindrical in shape, and they are sometimes somewhat compressed. The cypselae have eight 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, sometimes irritating enough to force florists to change occupation.
Solidago species are easily recognized by their golden inflorescences 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 the weather is warm and sunny.