Solidago gigantea
(giant goldenrod)

S. gigantea has spread in a number of European countries after introduction as an ornamental plant from its native North America. It continues to be available as an ornamental from mail-order catalogues and web-sites of commercial nurseries and botanical gardens. Morita (2002) indicates that S. gigantea is less noxious than S. altissima, but it is an undesirable invader on account of its large rhizomes and vigorous growth leading to gross changes in the native vegetation and fauna. S. gigantea is not a serious weed in annual crops since it can be controlled by tilling. However, it invades poorly managed pasture and can be a considerable weed in forest nurseries and in perennial gardens and crops.

S. gigantea is native to the USA and Canada, between the latitudes 30°N and 55°N, and introduced to Europe and temperate parts of Asia. The zonal amplitude stretches from the meridional to the subboreal belt in the eastern part of the European range (Meusel and Jäger, 1992).

S. gigantea is a widespread wild and ornamental plant in Europe. After its introduction it has shown itself well able to naturalize in temperate regions of the world. In Switzerland, this species is on the 'black list', i.e. neophytes whose negative ecological impacts have been documented, and which are problematic from a conservation point of view (CPS-SKEW, 2003).

S. gigantea is a forb growing in a wide range of different soil conditions but is not shade tolerant (Ellenberg et al., 1992). In its native range grows mainly in forest edges and roadsides, secondary old-fields and unmanaged areas where it colonized after establishment in a short time. In central Europe, S. gigantea is widely naturalized and is found in uncut grasslands, wetland edges, riparian habitats, forest edges, and along road sides (Hartmann and Konold, 1995; Botta-Dukát and Dancza, 2001; Weber, 2003).

In its native range, S. gigantea can occur in any crop; however, it is not a serious weed in annual crops since it can be controlled by tilling. However, it invades poorly managed pasture and can be a considerable weed in forest nurseries and in perennial gardens and crops.

Genetics

S. gigantea shows variation in chromosome numbers with three different cytotypes in its native range. They are listed below according to the nomenclature of Beaudry (1963, 1974); throughout this datasheet, S. gigantea represents the whole S. gigantea complex:

S. gigantea, 2n = 2x = 18 (trichomes on midveins)
S. serotina, 2n = 4x = 36 (glabrous narrow leaves)
S. shinnersii, 2n = 6x = 54 (glabrous wide leaves)

Beaudry (1974) distinguished a further, tetraploid variety, S. serotina forma huntingdonensis, defined by trichomes uniformly covering the lower leaf blade. In contrast, Melville and Morton (1982) find the cytotypes to be morphologically inseparable because of overlapping variation, although there might be a tendency for stronger leaf serration and pubescence in the diploid S. gigantea (Morton, 1984). Therefore, all cytotypes are treated as a single species by Morton (1984), despite being genetically separated.

In Europe, only the tetraploid form is widespread (Schlaepfer et al., 2008; 2010).

In north-east America, the hybrid S. canadensis L. x S. gigantea Ait. has been reported, which has also been identified in France (Wagenitz 1979). In nurseries, S. ptarmicoides (Torrey & A. Gray) B. Boivin (Syn.: Solidago asteroides, Aster ptarmicoides) has occasionally been observed to cross with various Solidago species, among them S. canadensis, the hybrids are known as Solidaster (Schillinget al., 2008).

Microsatellite primers for S. gigantea have been developed (Beck et al., 2014).

Physiology and Phenology

The germination of achenes and the storage carbohydrates of the rhizomes of this species were investigated in samples collected from 16 locations in Hungary in 1998, to study the contribution of these characteristics to the invasiveness of this species (Szabó and Balogh, 2000). Good achene germination was recorded (20-30% germination), especially during spring, but the germination of samples from different locations was highly variable (Laszlo and Lajos, 2000).The germination is frequent in abandoned fields and unmanaged grasslands. The most suitable conditions for germination are the surface of undisturbed soils and gaps in uncut grasslands. In the rhizomes, free sugars were present in early autumn, especially sucrose and fructose, and fructan storage polymers were accumulated in the rhizome during autumn (Szabó and Balogh, 2000). Biomass production was determined mainly by water supply, especially by the rainfall in the first part of the growing season. Early in the growing season, the time of shoot initiation is determined by temperature. The plants responded to summer drought by reducing their leaf area. The rate of leaf decline is influenced by the amount of rainfall, although rainfall has no effect on the formation of leaves. The size and thickness of leaves decreases during the season but the number of leaves does not change considerably; the reduction of leaf area is caused by the diminution of leaf size (Dancza and Botta-Dukát, 2000; Botta-Dukát and Dancza, 2001).

S. gigantea contains various compounds including terpenoids, phenolic compounds, coumarines, polyacetylic substances, polysaccharides, essential oils and diterpenebutenolides (Gerlach, 1965; Jurenitsch et al., 1988; Johnson et al., 2007). The roots contain large amounts of furanoid compounds and acidic compounds (solidagoic acids) (Anthonse et al., 1973). The hydrodistilled essential oil of aerial parts of S. gigantea contains up to 90 constituents (Kalemba et al., 2001). The saponins of S. gigantea have been analysed by Jurenitsch et al. (1986) and Reznicek et al. (1996).

Reproductive Biology

S. gigantea is a rhizomatous hemicryptophyte and has a complex life cycle with rhizome and seed propagation. Seeds of European plants do not show dormancy and do not need scarification or stratification. (Voser-Huber, 1983). The fruit of S. gigantea is an achene with attached pappus. The major pollinating agents of S. gigantea are honeybees (Apis mellifera), bumblebees (Bombus spp.), soldier beetles (Chauliognathus pennsylvanicus) and syrphid flies. Although seeds are essential for long-distance dispersal and the colonization of unoccupied sites, they are not important for the spatial extension of established populations. Intensive shoot growth starts in April and shoot height increases nearly linearly until the end of July when final height is achieved. Inflorescences are formed from June onwards. Peak flowering time is between mid-August and end of September, but flowering can continue through October in central Europe. Seeds are easily dispersed by wind, but only in dry weather conditions. Rhizome buds are formed during the summer and grow to rhizomes in autumn. Occasionally, rosettes may be formed in autumn, but normally rhizomes produce shoots in spring of the following year. The main growth period for rhizomes is late summer and autumn.

Environmental Requirements

The habitat preferences of the North American Solidago species are wide. S. gigantea prefers heavy soil types and wetland edges. It usually colonizes semi-natural habitats and often occurs on riverbanks in central Europe. It establishes well in disturbed sites and becomes dominant due to extensive vegetative spread. In the exotic range in Hungary, S. gigantea proved to be a more successful invader than S. canadensis/S. altissima, whereas these species have a wider natural geographical distribution than S. gigantea in their native North America (Dancza and Botta-Dukát, 2003).

Associations

S. gigantea is a characteristic species of nitrophilous communities with tall forbs along riverbanks (Class Artemisietea; Ellenberg et al., 1992). Tüxen (1950) distinguished a Rudbeckia laciniata-Solidago canadensis association and Moor (1958) described the Impatienti-Solidaginetum and Impatienti-Solidaginetum associations. S. gigantea forms extensive stands in Onopordetalia-, Aegopodion- and Alliarion communities and penetrates into abandoned Arrhenatheretea meadows (Oberdorfer, 1994). In Hungary, S. gigantea is a character species for other associations, Agropyro-Solidaginetum and Eupatorio-Solidaginetum (Kovács, 1994).

A great diversity of insect herbivores attack S. gigantea in its native range. Meyer et al. (2005) observed over 20 different insect taxa in 5 orders feeding on plants in a garden over a 2 year period. These included spittlebugs (Philaenus spumarius), aphids (Uroleucon caligatum and U. nigrotuberculatus), beetles (Trirhabda virgata, Exema canadensis), various caterpillars, various leaf mining and leaf galling insects (including Asteromyia sp.), and other gall-making insects (Epiblema scudderiana, Gnorimoschema gallaesolidaginis, Rhopalomyia sp). The goldenrod ball gall (Eurosta solidaginis) is also known to occur on S. gigantea (Abrahamson et al., 2001).

The insect fauna of S. altissima (as S. canadensis var. scabra), S. fistulosa, S. gigantea and S. leavenworthii was surveyed in 1981-84 in and around Gainesville, Florida, USA. The 122 phytophagous species collected are listed and classified according to relative frequency of occurrence, guild, host range, plant part attacked, life stages collected, and associated Solidago species. Only 14 (11%) of the phytophagous species are known to be restricted to Solidago and Aster (Compositae). There were eight insect species considered as possible biological control agents of Solidago spp. Eurosta sp. attacking roots, two leaf chewers Ophralella sexvittata and Sparganothis distincta, two leaf miners Agromyzidae sp. and Cremastobombycia solidaginis, a leaf galler Asteromyia carbonifera, and Schizomyia racemicola and Schinia nundina attacking flowers and seeds (Fontes et al., 1994).

Heteropteran species attacking S. gigantea in the Czech Republic have been reported by Rohacova and Drozd (2009)

Foliar pathogens attacking S. gigantea in North America include a rust fungus (Puccinia dioicae), a powdery mildew (Erysiphe cichoracearum), and a bacterial pathogen (Xanthomonas sp.) (Meyer et al., 2005). A powdery mildew (Golovinomyces asterum var. solidaginis) has been reported on S. gigantea in Korea (Cho et al., 2013).

S. gigantea has a rich herbivore fauna in its native range but experiences very little herbivory in its introduced range. Jakobs et al. (2004) found that a majority of surveyed S. gigantea populations in North America had herbivore damage, compared to virtually no signs of herbivory in European populations. Plants in Europe were also larger and grew at greater density than plants in North America, suggesting that reduced herbivory may contribute to the invasiveness of S. gigantea in Europe. Several garden experiments have explored whether release from herbivory in the introduced range has resulted in evolution of reduced defenses and/or greater investment in growth and reproduction in European plants. There is evidence that European plants have lower levels of anti-herbivore defenses compared to North American plants: they have lower foliar concentrations of monoterpenes and diterpenes, supported better performance of a generalist caterpillar, and were more susceptible to foliar pathogens (Meyer et al., 2005; Johnson et al., 2007, Hull-Sanders et al., 2007). European plants also tended to be larger than North American plants when grown in gardens (Güsewell et al., 2006; Meyer and Hull-Sanders, 2008). Although European plants produced more inflorescences than North American plants in a European garden (Güsewell et al. 2006), in a North American garden European plants were less likely to flower and showed a greater investment in rhizome biomass compared to inflorescence biomass than North American plants (Meyer and Hull-Sanders, 2008).

General

• Botanical garden/zoo

Medicinal, pharmaceutical

• Traditional/folklore

S. gigantea is distinguished from its closely related S. canadensis by having glabrous and glaucous stems. The shoots of S. canadensis are at least weakly hairy. The calyxes of ligule flowers of S. gigantea are longer than the tubular flowers of S. canadensis. S. gigantea has bright yellow flowers and the pappus is brownish-white, whereas the flowers of S. canadensis are somewhat lemon-yellow and the pappus silvery whitish.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control

The enormous infested grassland areas are effects of the poor previous management practices, and in grasslands, continuous mowing or grazing is necessary every year to prevent establishment of Solidago species.

Mechanical Control

Systematic mechanical control such as mowing is effective against Solidago species, and at least two mowings per year of the infested area are necessary. During restoration of grasslands, continious mowing can prevent flowering and rhizomes developing in the winter and during periods of vegetative growth.

Hartmann and Konold (1995) found that effective measures to reduce shoot density and vitality include mowing once a year and mulching, or mowing twice a year without mulching, over a period of 3 years.

Chemical Control

Germinating and young plants are sensitive to soil herbicides, but later, during the vegetative period, soil herbicides are ineffective. At heights of 10-15 cm, glyphosate, 2,4-D and several contact herbicides are suitable for the control of S. altissima. Herbicide use is required to control the weed in forest nurseries.

Biological Control

Although a number of natural enemies have potential as biocontrol agents (see Notes on Natural Enemies), none have been fully proven and developed (Sheppard et al., 2005).

22/04/14 Updated by:

Gretchen Meyer, University of Wisconsin-Milwaukee, USA