As previously indicated, a number of weed species are especially troublesome because they are poisonous to humans and/or animals. The table below summarizes the names, toxic compounds, and species affected for a number of important poisonous plants found in the U.S.
| Poisonous species | Toxin | Symptoms of Poisoning |
|---|---|---|
| Larkspur | Alkaloids | Nervousness, staggered gait, bloat, sudden death |
| Lupines | Alkaloids | Birth defects (e.g. crooked legs), convulsions, loss of muscular control |
| Water hemlock | Cicutoxin | Sudden death |
| Locoweed | Alkaloids, Selenium | Nervousness, staggered gait, bloat, sudden death |
| Halogeton | Oxalates | Weakness, salivation, increased heart rate |
