Ask Mr. Smarty Plants

In North America there are few plants that have poisonous thorns.  The members of the Solanum (nightshade) genus have thorns and are reported to cause injuries that are slow to heal due to poisonous thorns.  Many members of the nightshade family (Solanaceae) have many poisonous parts (i.e. leaves, stems, fruit, roots, seeds) that cause severe irritation to mammals.  The members of this family are widely distributed across North America. 

Another group of plants that have poisonous “thorns” is Stinging Nettles.  They have tiny hairs on the underside of their leaves that ‘sting’ and cause skin irritation and a burning sensation if they are brushed against. 

Finally, most plants that have thorns can cause mechanical injury, and some injuries result in pieces of the thorn breaking off in the skin.  It would seem as if these plants had poison, but in fact, the swelling and redness around a wound is caused by a foreign object logged in the skin. 

Considering plants outside of North America there are several plants from Africa that have poisonous thorns such as Gymnosporia buxifolia or Dichrostachys spp. 

I acquired my information about thorny plants from the Botanical Dermatology Database.  There is lots of information there if you would like to read further about the affects of plants with thorns.