• The berries of the flowering dogwood contain poison.Comstock/Comstock/Getty Images
  
  Exploring woods and fields is a favorite pastime for both pure nature lovers and amateur botanists. However, you need to take care when exploring your local landscape, as many of the common trees and plants found in the U.S. are poisonous. Degrees of toxicity vary from one species to another. For example, some plants are only poisonous to livestock, while others, such as black walnut, are poisonous to other plants. Additional toxic plants include species such as the lovely flowering dogwood and common nightshade, a poisonous vine.
  
  

Flowering Dogwood

• The flowering dogwood (Cornus florida) is a popular landscaping tree often planted as an ornamental. With its lovely pink or white blossoms, brilliant scarlet fall foliage and graceful shape, it's easy to understand the popularity of this tree. The tree has medicinal uses as well. During the Civil War, digitalis was extracted from dogwood bark and used as a quinine substitute for treating malaria. On the negative side, the USDA Plant Guide for the tree states quite clearly that its red berries contain chemicals that are poisonous to humans.
  
  

Black Walnut

• The black walnut tree (Juglans nigra) is highly valued both as a source of premium-grade furniture lumber and tasty walnuts. In the wild, the trees often form pure stands due to the presence of a toxin known as "juglone," which is found the black walnut's buds, roots and nut hulls. This chemical slows the growth of surrounding plants, thus reducing competition for light and water. Juglone saps the strength of other trees, robbing them of the energy needed to perform photosynthesis. Trees affected by juglone gradually begin to yellow, wilt and eventually die. The USDA Plant Guide for this tree cautions that its bark is poisonous to humans.
  
  

Black Locust

• Black locust (Robinia pseudoacacia) is a native hardwood and a member of the legume family, and is valued as a source of timber and for its erosion-control capabilities. According to the poisonous plants database maintained by the Cornell University Department of Animal Science, the leaves, bark and seeds are poisonous to livestock, particularly horses, as well as humans. Oddly enough, honey produced from the nectar of black locust blossoms is not poisonous. It is both delightfully sweet and fragrant.
  
  

Common Nightshade

• Common nightshade (Solanum nigrum), which is also known as horse nettle, is a toxic alien vine. As such, it is often found growing up the sides of pasture posts for support. The leaves and immature berries of the plant contain two separate poisons, soladulcidine and solanine. These chemicals are toxic to horses, cattle, small rodents and humans.