- Name also: Giant Golden-rod, Tall Goldenrod, Late Goldenrod, Smooth Goldenrod
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Perennial herb. Rhizomatous, forms stands.
- Height: 50–250 cm (20–100 in.). Stem glabrous till inflorescence, often blue-grey at base.
- Flower: Flowers form approx. 1 cm (0.4 in.) wide, single flower-like capitula surrounded by involucral bracts. Capitulum flowers yellow, ray-florets tongue-like; disk florets tubular, small. Stamens 5. Gynoecium composed of 2 fused carpels. Involucre round, 3.5–5 mm (1.4–2 in) long, involucral bracts overlap in several rows. Capitula form conical, densely branched racemes, branches quite erect, quite often straight and finely haired.
- Leaves: Alternate, stalkless, dense. Blade narrowly elliptic, tapering base, sparsely sharp-toothed, upper ones with quite entire margins, upper side glabrous, underside shortly haired parallel with veins.
- Fruit: Cylindrical achene with downy tip.
- Habitat: Meadows, waste ground, yards, roadsides, railway embankments, waterside thickets. Also ornamental.
- Flowering time: August–October.
- Harmfulness: Harmful invasive species.
The genus Goldenrod includes around a hundred species, almost all of which are native to North America. The only natural inhabitant of the old world seems to be familiar goldenrod (S. virgaurea; also known as woundwort). Thanks to human involvement, the number of Finnish goldenrod species has increased by a few species that were originally brought here as ornamentals. These include handsome giant goldenrod, which can grow up to 3 metres (10 feet) tall and develops a dense conical compound cyme with a myriad of small yellow capitula. Giant goldenrod is very like its relative, Canada goldenrod (S. canadensis), which is an even more common feature of flower beds. The flowerless stem of giant goldenrod is more rigid and is glabrous below the inflorescence. The inflorescence branches are denser, shorter and more erect, and the capitula are bigger.
Both goldenrods have escaped from gardens, although giant goldenrod has made it over the fence with noticeably less success than its relative. Giant goldenrod’s seeds are able to ripen in Finland only in exceptionally warm summers. When that happens the autumn inflorescence looks fluffy due to the flying hairs. As the climate becomes warmer and the growing season lengthens, the possibility to spread increases. Keeping goldenrods under control could therefore become extremely difficult because they produce a huge amount of seeds, up to 10,000 on each shoot. They can travel long distances on the wind, unlike e.g. lupin seeds, which are large and fall in the same growing area. The rigid stems survive long into the winter, when cypselas with flying hairs can spread over the snow with fewer obstructions than they face in summer. When fast-growing giant goldenrod escapes into the wild it can get the better of many Finnish wildflowers and threaten the original diversity of our nature. Giant goldenrod that is currently growing in yards need not be given a death sentence however, it is enough to cut the flower stems before the seeds ripen, so they are a good choice for the flower vase. About 5 other large North American goldenrods grow in Finnish gardens, along with hybrids between these, especially garden goldenrod varieties that have been developed from Canada goldenrod.