Impatiens glandulifera

The plant grows up to 2 m tall, usually unbranched and hairless, with bright pink flowers in upright racemes of 5 to 20 and a curved spur.

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

In Switzerland it grows on stream banks and in floodplain forests, has been naturalised since about 1920 and is still spreading; it comes from the Himalaya.

BfN describes its rich nectar supply as the reason it attracts flower visitors, above all bees and bumblebees.

In an Irish riverside study, Himalayan balsam secreted nectar faster and with higher sugar concentration than native hairy willowherb and marsh woundwort, and long tongued bumblebees such as Bombus hortorum chiefly visited it.

In Austrian citizen science pollen traps, Impatiens pollen ranked fifth among pollen types collected by honey bees in August and September, at 6.1 percent of grains.

In a Bavarian LWG trial on late forage, colonies placed at a Himalayan balsam site collected mostly Phacelia pollen; balsam family pollen averaged only four percent.

Since 2017 Impatiens glandulifera is on the EU list of invasive alien species of Union concern, added by Commission Implementing Regulation (EU) 2017/1263.

In Switzerland it is a Black List species and stands on the list of banned organisms of the Release Ordinance.

Along watercourses it displaces native bank vegetation; one plant makes up to 2,500 seeds and the exploding capsules throw them up to 7 m.

The German BfN handbook says the species was often spread deliberately as a bee forage plant and is now widespread and common in Germany.

BfN advises that beekeepers should not sow the plant outside settlements and that control should aim to prevent seed set, starting when the first flowers appear in late July.

In Czechia it is an invasive neophyte recorded in 531 grid cells, among the twenty most widespread invasive taxa.

The University of Innsbruck notes that the plant reached Europe in 1839 as an ornamental and bee forage plant, now climbs to about 1600 m in Tyrol, and that its mass stands reduce diversity and raise erosion risk.