Solidago canadensis

The plant is 50 to 200 cm tall, branched only in the inflorescence, with yellow flower heads 3 to 5 mm across in a one sided terminal panicle.

Info Flora gives the flowering period in Switzerland as July to September.

In Switzerland it is naturalised in forest clearings, river bank scrub and waste ground from the hill to the montane zone; it is originally North American.

The Info Flora sheet cites a 1979 Tyrolean study in which honey bees preferred Canadian goldenrod over the native European goldenrod Solidago virgaurea.

BfN states that the flowers are pollinated by bees and bumblebees and in late summer feed numerous wild bees, butterflies and hoverflies.

In wet meadows in the Vistula valley near Krakow, Poland, the abundance and species richness of bees and butterflies fell non linearly once invasive goldenrod (Solidago canadensis and S. gigantea) cover passed about 50 percent for bees and 30 to 40 percent for butterflies.

Info Flora advises cutting the flower heads before fruiting and not putting cuttings on garden compost; it notes the plant is very popular in gardens.

The Info Flora sheet lists Canadian goldenrod as a species with a handling ban under Annex 2.1 of the Swiss Release Ordinance.

One plant can produce more than 10,000 wind dispersed seeds, and the rhizome system builds extremely dense stands with up to 300 stems per square metre.

BfN says the species has been known from England since 1645, was widely planted in gardens and as bee forage in the open landscape, and is among the most frequent neophytes in Germany.

Goldenrods form dense stands by clonal rhizome growth, and light loving plant species are displaced by their dominance stands.

Only repeated mowing pushes goldenrods back in the long term, according to BfN.

In Czechia Solidago canadensis is an invasive neophyte present in 82.2 percent of mapping grid cells, among the most widespread alien plants.

In Tyrol goldenrods have been present since about 1900; each inflorescence can form up to 20,000 winged seeds and the plant regenerates from the smallest rhizome pieces.