The Solidago genus

Next up in my short series of posts about non-indigenous species is a couple of plants from the genus called goldenrod (Solidago). In today’s English exercise I explore characteristics of two very similar species with golden-yellow flowers and some minor differences between the two. Canadian goldenrod (Solidago canadensis) and giant goldenrod (Solidago gigantea) are both perennial plants, native to North America (as one of the names suggests), but invasive in our environment – because they spread very quickly and form massive stands, endangering local vegetation. They were brought to Europe as an ornamental plant. Solidago genus is part of Asteraceae (Compositae) family.

Let’s begin with the characteristics that these two species have in common. They both grow really tall, up to 2,5 meters. Leaves are alternately arranged, they have lanceolate (prolonged) shape with serrated margins (teeth on the edges). They can be sessile (attached to stem without petioles) or petiolated; with only short petioles. Flowers of course get most of our attention, and their color and smell also attract bugs – they blossom from July till October. Flowers are gathered into large yellow inflorescence that consists of numerous calathidiums. The outer flowers of calathidium are called ligulate flowers (ray florets) and the inner are tubular flowers (disk florets). (Such composite flowers are quite typical for plants in Asteraceae family.) Fruit in the form of achene ripens in the fall and it is “equipped” with pappus (lint) hairs that help carry its one seed far away in the wind. Seeds are one way of propagating for Solidago plants, but they also owe their success to rhizomes (underground stems) which enable them to spread wide.
Solidago canadensis and Solidago gigantea grow on riverbanks and forest edges, we can see them along the railroads and in other ruderal habitats… Although they can supplant other (native) plants, I often saw them in a company of another (alien) species, Himalayan balsam (Impatiens glandulifera) – they seem to get along just fine?
zlata-rozga-zlezava-nedotika

Moving on to how we can tell Canadian and giant goldenrod apart. One of the differences is the size of the flowers … Giant goldenrod’s calathidiums are for about one millimeter larger than its cousin’s. Giant goldenrod also has ligulate flowers longer than tubular flowers; while Canadian goldenrod has tubular and ligulate flowers of the same length. If we look really close and focus, we’ll probably see the difference. But there’s also another feature, a bit easier to spot. Canadian goldenrod has pubescent, hairy stem and leaves, while its giant relative usually has no (or at least very little) hair (trichomes); that’s why it is also called smooth goldenrod.

I took the following pictures last autumn. Unfortunately, they don’t all precisely show subtle distinctive features of Canadian and giant goldenrod – so I present them in a “broader sense”, as goldenrod genus. This can at least serve for recognition of these plants; and observing them in all the detail when coming across them “in situ”.

zlata-rozga-cvet
Goldenrod flowers.

zlata-rozga-zorenje
Goldenrod flowers and development of fruit.

zlata-rozga-jeseni
Goldenrod fruit.

zlata-rozga-macek
More about this cat (and goldenrod) here.

Did you know? One of the species of Solidago genus is native to our country. Solidago virgaurea is used in herbal medicine and is supposed to help with bladder and ureter problems.


Sources:

* Cvetlice : enostavno in zanesljivo določanje (Kranj, 2006).
* Margot in Roland Spohn, Katera cvetlica je to? (Olševek, 2008).
* Rastlinski vodnik (Ljubljana, 2008).
* Francesco Bianchini in Azzurra Carrara Pantano, Vse o cvetju (Ljubljana, 1978).
* Dr. Jörg Grünwald in Christof Jänicke, Zelena lekarna (Ljubljana, 2007).
* https://www.tujerodne-vrste.info/vrste/kanadska-zlata-rozga/ and https://www.tujerodne-vrste.info/vrste/orjaska-zlata-rozga/
* https://www.ljubljana.si/sl/moja-ljubljana/varstvo-okolja/invazivne-tujerodne-vrste/invazivne-tujerodne-rastline/orjaska-in-kanadska-zlata-rozga/
(N. B.: information on removing and handling these plants.)

* Botanični terminološki slovar, https://isjfr.zrc-sazu.si/sl/terminologisce/slovarji/botanicni (really valuable for checking english and slovene terminology).
* https://www.cabi.org/isc/datasheet/50599 and https://www.cabi.org/isc/datasheet/50575
* https://gobotany.nativeplanttrust.org/species/solidago/canadensis/ and https://gobotany.nativeplanttrust.org/species/solidago/gigantea/