Solidago, commonly called goldenrods, is a genus of about 100[1] to 120[2] species of flowering plants in the family Asteraceae. Most are herbaceous perennial species found in open areas such as meadows, prairies, and savannas. They are mostly native to North America, including Mexico; a few species are native to South America and Eurasia.[1] 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 range from decumbent (crawling) to ascending or erect, with a range of heights going from 5 cm (2.0 in) to over a meter. Most species are unbranched, but some do display branching in the upper part of the plant. Both leaves and stems vary from glabrous (hairless) to various forms of pubescence (strigose, strigillose, hispid, stipitate-glandular or villous). In some species, the basal leaves are shed before flowering. The leaf margins are most commonly entire, but often display heavier serration. Some leaves may display trinerved venation rather than the pinnate venation usual across Asteraceae.[1] The flower is also the state flower of Kentucky.
The flower heads are usually of the radiate type (typical daisy flower heads with distinct ray and disc florets) but sometimes discoid (with only disc florets of mixed, sterile, male and types). Only ray florets are female, others are male, hermaphroditic or entire sterile. Head involucres are campanulate to cylindric or attenuate. Floret corollas are usually yellow, but white in the ray florets of a few species (such as Solidago bicolor); they are typically hairless. Heads usually include between 2 and 35 disc florets, but in some species this may go up to 60. Filaments are inserted closer to the base of the corolla than its middle. Numerous heads are usually grouped in complex compound inflorescences where heads are arranged in multiple racemes, panicles, corymbs, or secund arrays (with florets all on the same side).[1]
Solidago cypselae are narrowly obconic to cylindrical in shape, and they are sometimes somewhat compressed. They have eight to 10 ribs usually and are hairless or moderately hispid. The pappus is very big with barbellate bristles.[1]
The many goldenrod species can be difficult to distinguish, due to their similar bright, golden-yellow flower heads that bloom in late summer. 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.
The section Ptarmicoidei is sometimes treated as a separate genus Oligoneuron,[3] and is dropped by flat-topped to rounded corymbiform flowerheads.