Lysimachia vulgaris

Lysimachia vulgaris (yellow loosestrife) is a perennial wildflower, with hairy green leaves and clusters of bright yellow summer flowers. It does best in boggy soils such as the edge of ponds, and is considered a marginal plant. It spreads by creeping rhizomes and can be invasive – in countries where it has been introduced, including North America, it's considered a problem plant.

Despite having similar common names, yellow loosestrife is not closely related to purple loosestrife. However, it is closely related to another plant called yellow loosestrife, Lysimachia punctata, which is similar looking but has its flowers arranged in terminal clusters (at the top of the stem), is more tolerant of dry soil and is considered less invasive.

The name "Loosestrife" literally means to "lose strife". Plants in the genus are said to have calming properties, and are named after King Lysimachus, the King of Macedonia, who fed 'loosestrife' plants to his cows when they became agitated. Loosetrifes were also hung around the necks of cows to deter flying insects, and were also brought into homes and burned to get rid of infestations of flies.