Solidago, commonly called goldenrod, is a genus of about 100 to 120Solidago. Flora of China. 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. Some American species have also been introduced into Europe and other parts of the world.
Description
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 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.
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).
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.
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, and is dropped by flat-topped to rounded corymbiform flowerheads.
Taxonomy Solidago is in the family Asteraceae (formerly known as Compositae), a diverse and widespread clade containing approximately 23,000 species and 12 tribes, which inhabit all continents except Antarctica. Within Asteraceae, Solidago is in the tribe Astereae and the subtribe Solidagininaeae.
The genus Solidago is monophyletic as indicated by morphological characters and molecular evidence. All Solidago species are herbaceous perennials, growing from approximately to tall. Yellow to white, pistillate ray flowers and yellow, perfect disc florets are characteristic of Solidago inflorescences, which have a wide range of shapes. Molecular studies using nuclear rDNA have hypothesized boundaries on the genus Solidago, but there have been difficulties in parsing out evolutionary relationships at the sub-genus scale and defining which should be included and separated from Solidago.
Solidago and related taxa Related Asteraceae genera, such as Chrysoma, Euthamia, and Oreochrysum, have been included within Solidago at one point or another, but morphological evidence has suggested otherwise. In a study comparing morphological characters of Solidago and related subgroups, the authors consider the subjectivity of classifying a genus and how to define it within broader tendencies concerning the taxonomy of North American Asteraceae. Little to no differences were observed between Solidago and the subgroups in terms of karyotype. However, external morphological characters such as habit, or the general appearance of the plant and how a suite of traits contribute to its phenotype; pappus size; and the point of freeing of stamen filaments from the corolla tube, are useful classification schemes for Solidago, since they are applied to differentiating between Asteraceae taxa. One school of Asteraceae taxonomy thought unites all taxa sharing similar floral head structure and subsequently ignores deviation from this morphology, while another places greater weight on these morphological deviations. The authors argue that the latter opinion should be applied. Since there is no theoretical foundation for relative taxonomic importance of traits, they assert that habit should be a central trait when defining taxa, and subsequently that all the subgroups considered in their study (Brachychaeta, Chrysoma, Euthamia, Oligoneuron, and Petradoria) should be segregated from Solidago.
Results from a leaf anatomy study comparing differences in mesophyll, bundle sheath extensions, and midvein structure, among others in a suite of leaf traits, are incongruent with those in an earlier study. Based on the lack of bundle sheath extensions, it is suggested that Chrysoma, Euthamia, Gundlachia, and Petradoria should be distinct taxa and outside of Solidago. However, Brachychaeta, Brintonia, Oligoneuron, Oreochrysum, and Aster ptarmicoides should be considered as components of Solidago. To summarize, the relation of Brachychaeta and Oligoneuron to Solidago is inconsistent based on these results. Both support the separation of Chrysoma, Euthamia, and Petradoria from Solidago. A study reviews the taxonomic position of Oligoneuron relative to Solidago, as based on taxonomic evidence, treats it as separate from Solidago, similarly to Kapoor & Beaudry (1966). The first molecular phylogeny based on chloroplast DNA treats Brachychaeta, Brintonia, Oligoneuron, and Oreochrysum as constituents of Solidago. Using consensus trees from ITS data, another study found support for Oligoneuron as part of Solidago, and the findings of Zhang (1996). More recently, an analysis of combined ITS and ETS data provided additional support for the inclusion of Oligoneuron as part of Solidago.
Until the 1980s, the genus Euthamia was largely considered to be a part of Solidago due to morphological similarities between species in both genera, and a history of synonymy of Solidago lanceolata and Euthamia graminifolia. As mentioned, the lack of bundle sheath extensions in Euthamia compared to Solidago, and deviations in floral morphology present evidence for separation of these taxa. A taxonomy of Euthamia as a genus was presented, providing a detailed description of distinguishing external morphological characters, such as fibrous-roots, sessile leaves, and mostly corymbiform inflorescences.
Evolutionary relationships within Solidago Chromosome counts and advances in molecular systematics have enabled greater understanding of evolutionary relationships within Solidago. At the time a taxonomy of Solidago was published, related taxa causing contention, such as Chrysoma, Euthamia, Oligoneuron, and Petradoria, were excluded from this genus. The number of Solidago species has remained relatively stable, around 120, with approximately 80 in North America. Due to monophyletic support for the New World taxa and taxonomic difficulties with Old World taxa, the taxonomy provided in the 1990s only includes North American taxa and thus treats Solidago as non-monophyletic. Existing molecular-based phylogenies provide monophyletic support for Solidago given its inclusion of Oligoneuron.
Chromosome counts have proven to be a valuable character in Solidago taxonomy and in elucidating the cytogeographic history of the genus. Similar chromosome counts may indicate close evolutionary relationships, while different chromosome numbers may suggest distant relationships through reproductive isolation. Chromosome counts have been studied extensively in North America; all Solidago species have a base chromosome number of x=9, but the following ploidy levels have been observed: 2x, 3x, 4x, 6x, 8x, 10x, 12x, and 14x.
Though negligible differences in karyotype among Solidago and related genera were found, Solidago taxa with multiple cytotypes are more common than those with one. Although chromosome count is a useful metric for differentiating among Solidago taxa, it may be problematic due to the frequent variation in ploidy levels. Cytogeographic patterns in the Solidago gigantea complex, with tetraploids occurring in eastern North America and hexaploids in Oregon and Washington, were observed. Cytogeographic patterns are also observed in the Solidago canadensis complex: hexaploids within S. canadensis have been observed east of the Great Plains and are treated as Solidago altissima, and diploids and tetraploids occurring in the Great Plains are treated as Solidago gilvocanescens. The taxonomic status of Solidago ptarmicoides created an extensive debate due to frequency hybridization of S. ptarmicoides with members of the Ptarmicoidei section of Solidago. It was asserted that S. ptarmicoides should be united with Solidago rather than the genus Aster due to external morphological features such as similar pappus length as well as the same chromosome base (x=9). Information about chromosome number is still a crucial part of current understanding and phylogenies of Solidago.
Ecology Goldenrod is considered a keystone species, and has been called the single most important plant for North American pollinator biodiversity. Goldenrod species are used as a food source by the larvae of many Lepidoptera species. As many as 104 species of butterflies and moths use it as a host plant for their larvae, and 42 species of bees are goldenrod specialists, visiting only goldenrod for food. Some lepidopteran larvae bore into plant tissues and 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 ovipositors. Woodpeckers are known to peck open the galls and eat the insects in the center.
Goldenrods have become invasive species in many parts of the world outside their native range, including China, Japan, Europe and Africa. Solidago canadensis, which was introduced as a garden plant in Central Europe, has become common in the wild, and in Germany and Norway is considered an invasive species that displaces native vegetation from its natural habitat.
Use and cultivation Young goldenrod leaves are edible.Solidago missouriensis, Missouri goldenrod. Northern Rockies Natural History Guide. University of Montana, Missoula. Traditionally, Native Americans use the seeds of some species for food.Solidago nemoralis. Native American Ethnobotany. University of Michigan, Dearborn. Herbal teas are sometimes made with goldenrod.Goldenrod. Complementary and Alternative Medicine Guide. University of Maryland Medical Center.