Invasive species can outcompete native species and hurt local ecosystems. The Conservation Program removes invasive plants on Stanford lands, especially in sensitive habitats, to protect Stanford's biodiverse native ecosystems. You can help protect threatened species, reduce fire risk, and improve native biodiversity by joining us for a volunteer weeding day!
Sadly, there are many invasive species at Stanford. This list describes some of the most notorious invaders on Stanford lands, but there are many others:
Also known as: medusahead, medusahead grass
Identifying it: Medusahead is a thin grass with long, spiky heads that stays green after most other grasses have browned.
Why it's a problem: Medusahead creates a dense litter layer that's difficult for native grasses and other plants to break through. It increases summer fire risk and is largely unappetizing to native herbivores.
Also known as: wild mustard, black mustard
Identifying it: Wild mustard has clusters of tiny yellow flowers on top of long stalks (sometimes up to eight feet tall!) It commonly grows along roads and in open grassland areas.
Why it's a problem: Mustard's explosive seedpod bursting, chemical (allelopathic) exclusion of native plants, and increased fire risk for some California biomes makes it one of the worst invasives the Conservation Program fights. We've made dramatic progress removing it over the last few years, in particular inside Gerona Gate (the right side of the start of the Dish trail).
Also known as: scotch broom, common broom
Identifying it: Woody shrub with bright yellow flowers
Why it's a problem: Scotch broom can quickly crowd out native species and increase fire risk.
Also known as: periwinkle, big periwinkle, greater periwinkle
Identifying it: Vinca is a dark green vine with purple-blue flowers about the diameter of a golf ball. It makes itself at home in shady, damper areas, like the riparian zones around Stanford's creeks.
Why it's a problem: Vinca's vines form a dense mat which allows it to take over an area and block other plants from growing.
Also known as: Italian thistle
Identifying it: Italian thistle has purple flowers and broader, spiky leaves. It is one of the most common invasive thistles.
Why it's a problem: Italian thistle can grow densely and exclude native plants, especially in grassland ecosystems, oak savannas, chaparral, or along disturbed margins. It can worsen wildfire risk in spreading grassland fires into tree canopies.
Also known as: purple starthistle
Identifying it: Spiky green leaves and purple flowers surrounded by 'starlike' spikes.
Why it's a problem: Purple starthistle can quickly grow as tall as a person and choke out native plants.
Also known as: stinkwort, stinking fleabane
Identifying it: Dittrichia can look almost Christmas tree-shaped, with wiry, light green stalks growing up to a couple feet tall. It has small, pungent yellow flowers that resemble daisies.
Why it's a problem: Dittrichia's tens of thousands of wind-borne seeds and lack of appeal to grazing animals make it difficult to control. It has spread rapidly across California in just a few decades, and continues to spread today.
All other photos are creative commons photos with no attribution required or belong to the Stanford Conservation Program.