Identifying Goldenrods

Fall is in full swing and as the growing season winds to a close, one group of plants is still producing flowers and providing a last meal for pollinators preparing for winter. Many of the plants that bloom in the midwest this time of year belong to the sunflower family, Asteraceae. This plant family is extremely successful, containing over 23,000 species, the most species of any plant family (1). One reason this family is so successful may be due to the type of inflorescence these plants have – the capitulum.

This photo of silkgrass (Pityopsis sp.) shows a common arrangement of flowers in the Asteraceae flowers

This may surprise you, but flowers in this family such as daisies, dandelions, and sunflowers, are not actually flowers but inflorescences made up of many small flowers. In many of these plants what appear to be petals are actually sterile flowers (ray flowers) which are modified to look like petals and attract pollinators. The flowers in the middle (disc flowers) are typically the reproductive flowers that produce seeds. Capitula may contain only ray flowers (ex. dandelions), all disc (ex. thistles), or more commonly, a combination of disc and ray flowers.

Close up of goldenrod flowers. The flower on the right is a reproductive disc flower.

Goldenrods are a prolific group of plants in the sunflower family that help provide a last display of flowers before the onset of winter. Goldenrod flowers are almost exclusively yellow with a few species, such as silverrod (Solidago bicolor), having white flowers. Their peak bloom time coincides with fall allergy season, so these plants are often falsely accused of causing allergies. The real culprits of fall allergies are Ragweeds (Ambrosia sp., also in Asteraceae), which have wind pollinated flowers meaning they must release huge amounts of pollen into the air in hopes of reaching and pollinating other ragweed plants. This pollen is what gets up in peoples noses and prompts allergic responses. Goldenrods are insect pollinated and use their showy yellow flowers to attract bees and other pollinators. Because they can rely on helpful insects to transport their pollen, they don’t need to release as much as wind pollinated plants like ragweed. Stop blaming goldenrods for your allergies! They are innocent!!

Close up of giant ragweed (Ambrosia trifida) flowers, the true cause of fall allergies

There are over twenty species of goldenrod in Michigan. Due to the large number of goldenrod species and their similarity appearance, they can be tricky to tell apart. This is true for many groups of plants in the family Asteraceae. This family has a lot of terms for anatomy that are specific to this family (ex. pappus, involucres, phyllaries, etc.). There are many helpful resources for telling these plants apart. Michigan flora and the Manual of Vascular Plants of Northeastern United States and Adjacent Canada by Gleason and Cronquist are great guides if you living the midwest or surrounding areas and need an accurate ID. If you are just curious and want a rough idea of what species you may be looking at, the app Seek is a great option. However, as many goldenrod look extremely similar, sometimes these apps are not wholly accurate. Posting observations on iNaturalist can allow others with more expertise to give identifications. Just be sure to take closeups of all relevant plants parts including flowers, stems, leaves, and the full plant.

While working on identifying these goldenrods, I found some of the most helpful information to be the habitat the plant was growing in. Some plants prefer high quality wetlands, whereas others are quite weedy and will thrive along disturbed roadsides. A few species are easily distinguishable by appearance alone (Ex. Bluestem goldenrod, rough goldenrod, stiff goldenrod) but others are more tricky (Ex. Giant goldenrod, tall goldenrod, Canada goldenrod). This list details around half the goldenrods in my area.

Early Goldenrod (Solidago juncea) begins blooming in July before most other goldenrods. it has an open, spreading inflorescence. It grows in much of the eastern US and Canada and ushers in the goldenrod season. It can be found in disturbed gravelly roadsides, jack pine forests, and dry fields (2).

Bog Goldenrod (Solidago uliginosa) grows in bogs and fens and is able to hybridize with other wetland goldenrods like S. patula. This species is mostly hairless and the leaves are smooth and decrease in size from the bottom to top of the plant (2).

Hairy Goldenrod (Solidago hispida) has pubescent stems and leaves. This is not super helpful for identification as many goldenrods are hairy on different parts of the plant. Their leaves are oval and tend to be large at the base of the stem. They are sometimes considered the same species as S. bicolor, although S. bicolor has white flowers (2, 3).

Showy Goldenrod (Solidago speciosa) can occur in dry fields and prairies. Their inflorescences are not very branched, making it apparent where the name goldenrod comes from. The stems can be reddish and their leaves are toothless. Both stems and leaves are hairless (2,4).

Stiff goldenrod (Solidago rigida) is one of the more easily distinguishable species of goldenrod. It has thick leaves that are rounded and hairy. It can frequently be found in prairies and has a flat topped inflorescence with fairly large and showy capitula. A very good plant. Love and respect it.

Riddell’s Goldenrod (Solidago riddellii) thrives in high quality wetlands and wet prairies and is named after prolific botanist John Leonard Riddell. Its leaves are sessile, toothless, and tend to be somewhat folded inward along the mid vein. Sometimes this species is placed in the genus Oligoneuron with the other flat-topped goldenrods rather than Solidago (2).

Rough leaved Goldenrod (Solidago patula), also called swamp goldenrod, is another goldenrod which requires moist soils like those of fens and swamps. Its leaves are distinctively rough and more round than most species of goldenrod. I also think it’s kind of funny that the latin name can be abbreviated to S. patula. Like spatula. Heeheehee.

Canada Goldenrod (Solidago canadensis) is a common species and is easy to mistake for tall goldenrod (S. altissima) or giant goldenrod (S. gigantea). However, giant goldenrod has a smooth stem and tall goldenrod has longer Involucres. Canada goldenrod is a weedy plant growing in many different habitats. It is also considered an invasive species in some parts of Europe and Asia (2).

Blue stemmed goldenrod (Solidago caesia), unlike many of the other species of goldenrod which occur in Michigan, thrive in shady areas. This plant occurs in woodlands and the inflorescences appear in bunches along the stem in the axils of each leaf. It is an important fall food source for woodland pollinators.

Slender goldentop (Euthamia caroliniana) has one main vein on its leaves.
Grass leaved Goldenrod (Euthamia graminifolia) has three main veins on its leaves.

Besides Solidago, the closely related genus Euthamia is also referred to as goldenrods. Plants in this genus are known as grass-leaved goldenrods or goldentops. The two species of Euthamia which occur in Michigan can be distinguished from each other by looking at the number of leaf veins (2). Like Canada goldenrod and giant goldenrod, Grass leaved goldenrod (E. graminifolia) is invasive in Europe.

Florists sometimes sell goldenrod flowers under the name of their genus, “Solidago”, which is much more posh sounding. This is probably because many associate goldenrods with weediness and hay fever. Although many people overlook goldenrods as weeds, pollinators and other fauna rely on these plants as a late season food source. Insects may use the stems or leaves as places to lay their eggs forming round stem galls or odd poofy leaf galls. Birds can easily spot galls and peck into them for a tasty snack of larvae, or just eat the goldenrod seeds. On the whole, goldenrods are great contributors to their habitat and are very nice to look at so make sure to go out and admire them while you can.

Sources: 1, 2, 3, 4

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