You Will Get 5 Seeds Eucommia Ulmoides Hardy Rubber Tree. These unique trees actually contain a small amount of natural rubber in the leaves, and if you take a leaf and slowly pull it apart you can see the strands of rubber clinging to keep the two halves of the leaf together.. Now the rubber content of this species is much lower than that of the tropical rubber trees, but this is a very unique and cold hardy tree.. They are hardy to at least USDA zone 5, and possibly colder.. These plants would make excellent additions to your rare plant collection, or just make a unique statement in your yard.