• Ingesting an azalea plant may cause you to have toxic reactions.Jupiterimages/Photos.com/Getty Images
  
  In the United States, indoor plants are the third most common cause of poisoning in humans, after medicine and household chemicals, according to the University of Nebraska. If you own houseplants, you should find out whether or not your plants are poisonous. In addition, it may be helpful to know which parts of the plants are toxic and the symptoms that may occur if anyone in your household accidentally ingests the plants.
  
  

Whole Plant

• Many indoor plants are toxic all around; that is, if you ingest any part of the plant -- such as its leaves, seeds, bulbs, sap or berries -- you may become quite ill. If any section of an azalea plant (Rhododendron occidentale) is ingested, you may experience nausea, vomiting, breathing difficulty, loss of balance and dizziness, according to the Government of Alberta's Agriculture and Rural Development.
  
  While eating any part of the Jerusalem cherry (Solanum pseudocapsicum) can bring about toxic reactions, the most toxic parts of the Jerusalem cherry are its leaves and unripened fruit. Symptoms may include paralysis, loss of sensation, dilated pupils, digestive distress, respiratory and circulatory problems, and death.
  
  Lastly, the oleander (Nerium oleander) is a very poisonous houseplant -- eating just one leaf from this plant could be lethal. Within a few hours of ingesting the plant, you may experience an increased pulse rate, dizziness, drowsiness, weakness, cold extremities and digestive distress.
  
  

Leaves

• If you ingest the leaves of calla lilies (Zantedeschia aethiopica), you may experience a burning sensation and swelling of your mouth and throat as well as vomiting.
  
  Likewise, eating the leaves and buds of a hydrangea (Hydrangea macrophylla) may result in vomiting and breathing problems.
  
  The philodendron's leaves are also toxic and may cause burning of the mouth, lips, throat and tongue upon ingestion, according to the University of Wisconsin-Eau Claire. Skin irritation such as itchiness and reddening may also occur.
  
  

Bulbs

• Consuming the bulb of a tulip (Tulipa) or hyacinth (Hyacinth orientalis) may cause serious stomach cramping, vomiting and diarrhea.
  
  In addition to stomach pains and digestive problems, eating the bulb of a narcissus plant may result in trembling and convulsions. Ingesting the bulb of a narcissus is potentially fatal to humans.
  
  

Sap

• The sap of certain plants can be poisonous to humans. For example, if the sap of crown of thorns (Euphorbia milii splendens) or milk bush (Euphorbia trigona) gets onto your skin or into your eyes, you may experience skin or eye irritation. Ingesting the sap of either plant could make your tongue, mouth and throat swell up and cause vomiting.
  
  

Seeds

• Eating the seeds of the castor bean (Ricinus communis) could cause severe digestive problems, extreme thirst, vision changes, convulsions and possibly death. Castor bean seeds are so toxic that ingesting one to three seeds could be fatal for a child.
  
  The seeds of the bird of paradise plant (Strelitzia reginae) are also poisonous if ingested; drowsiness, dizziness, vomiting and diarrhea are some symptoms that may occur.
  
  

Berries

• Though a welcome house plant during the holidays, the mistletoe's (Phoradendron leucarpum and Viscum Album) berries may be toxic to human beings. When the berries of a mistletoe are ingested, stomach pains may occur; the intensity of the pain and severity of the poisoning will vary from one person to the next.
  
  If ingested, the green berries of the lantana plant can cause irritation in your stomach and intestines, circulatory problems, muscle weakness and even death.