A Word of Caution: Toxic Plants

Some plants are defending themselves from invaders with all their might. But it’s summertime, which leads us to spend more time outdoors. So, while communing with Mother Nature, one should be mindful of a few dangers of flora in the Willamette Valley.  

Tactile encounters or ingestion of some plants may result in a rash, but a few may present much graver consequences. 


Poison Hemlock or Hemlock (Conium maculatum) is an invasive, biannual plant often confused with wild carrot or Queen Anne’s Lace. It has white flowers gathered in umbrella-shaped clusters and lacy leaves. 

Its hollow stems can reach up to eight feet tall, but are not hairy like those of wild carrot, and are distinctly marked by purple blotches. 

It is said that Ancient Greeks used hemlock as a means to execute death row prisoners. Socrates allegedly consumed cicutoxin to end his life. 

Water hemlock, however, has been used in great dilution as homeopathic medicine.  

To eradicate either of the hemlocks, the plant requires digging or pulling it out without touching it to bare skin. It can be disposed of in a plastic bag. 

Cow Parsnip

Cow Parsnip (Heracleum lanatum) is another peculiar plant in the carrot family. It is a native species, present in pastures, meadows, and riparian areas. Although not nearly as toxic as hemlock, it can cause burning on contact, as it increases sensitivity to sunlight.  

It can grow up to 10 feet tall and bears white umbellate flowers; however, the leaves are not lacey like the hemlocks’, but palmate. 

Tansy Ragwort

Tansy Ragwort (Jacobaea vulgaris) is an invasive biannual that has bright, daisy-like yellow flowers and can grow two to four feet tall. It is tolerant of droughts and thrives in pastures where it can decimate cattle, sheep, or horses. The tansy blooms in June and July and the seeds spread easily, though it can be easily pulled or eradicated by spraying it with horticultural vinegar.  

According to OSU Extension Services,Tansy is mostly a weed that gets a foothold in plant communities that have been disturbed, either by grazing, logging, construction or fire.”  

In the 1960s, biocontrol of the plant was researched, and it was found that the cinnabar moth, flea beetle, and seed head fly were natural enemies of the noxious weed. These insects were then introduced into the areas in which tansy had grown. 

Pacific Poison Oak

Pacific Poison Oak (Toxicodendron diversilobum) is a cashew and sumac relative. It is a perennial plant with inconspicuous yellowish flowers and shiny, dark green, lobate leaves arranged in threes. The leaves turn red in the fall when the plant bears small, greenish berries. It can grow as a vine or shrub. Urushiol, present in every part of the plant, causes — in many mammals — mild to severe rash.  




Deadly Nightshade (Atropa belladonna) is another invasive species in Oregon. Atropine, which increases heart rate and is used for medicinal purposes, comes from this plant. 

As its name suggests, Deadly Nightshade is a highly poisonous plant; the toxin concentrates in black, shiny berries produced by purple and yellow flowers.  

Preferring shady sites, Deadly Nightshade is mostly found near bodies of water such as creeks, marshes, and wetlands. It can also survive along field edges, gardens, and roadsides. This herbaceous, perennial shrub stands about three to six feet tall.

For more info on how to distinguish Oregon’s poisonous plants, check out this guide from OregonLive. 

By Joanna Rosińska