My flowers were once yellow and sticky,
Without them, ID’ing might be a bit tricky.
But with some attention, it’s not a hard deed,
Just look out for my 3-capsuled seeds.
Common St. John’s Wort is a well-known plant used widely for its medicinal qualities. St. John’s Wort extracts are commonly found in pharmacies and are marketed for treating mild to moderate depression. Unfortunately, it is also an invasive species in the Sea to Sky area. While its chemicals may be helpful to us, its presence in our local ecosystems is not!
Native to Europe, North Africa, and West Asia, Common St. John’s Wort was originally brought to North America around 1700 for its medicinal properties and has grown out of control since. It thrives in dry, sandy soils and full sun. Common St. John’s Wort is often found in grasslands, forested areas, along roadsides, rail lines, and disturbed areas.
In summer, Common St. John’s Wort is easily identifiable due to its unique bright yellow flowers with numerous long, showy stamens. After maturing, the flowers form 3-chambered fruits that contain seeds. If squished while unripe, these sticky capsules release a red-staining liquid. After fully ripened, the seeds will drop from the fruits when the rest of the plant dies, in autumn.
Common St. John’s Wort reproduces mainly by seed, with each plant capable of producing 15,000-34,000 seeds. These seeds can remain viable in the soil for up to 10 years due to their gelatinous coating. However, this species can also form new individuals from its spreading rhizomes.
Common St. John’s Wort’s prolific seed production allows it to outcompete native species easily and persist through extreme conditions. This plant also contains a compound that can cause skin blistering in light-coloured livestock after exposure to the sun. Consequently, infestations cause food shortages for wildlife and livestock.
During the summer, Common St. John’s Wort is easily confused with Common Tansy and Tansy Ragwort, both of which also have bright yellow flowers. However, after flowers have matured into fruits and seeds, it’s much more easily confused with Wild Parsnip and Wild Carrot, as these species form umbrella-shaped clusters of oval seeds. Wild Carrot’s seeds, however, are covered in fine hairs, and Wild Parsnip is much larger than Common St. John’s Wort, growing up to 2 m tall rather than up to 1 m tall.
Per SSISC’s Invasive Plants Priority List, Common St. John’s Wort is listed as a species to strategically control throughout the Sea to Sky region. We rely heavily on reports from the public to understand the current distribution of plants in the Sea to Sky and prevent their spread. With that in mind, we invite you to keep your eyes peeled for Common St. John’s Wort and report any sightings.