Eidheann

From Temuairian Botany Book:

Medenia is a strange land. A plant commonly found around the Asilon region is used in a most peculiar way. It resembles what the tuatha called 'Eidheann', simply ivy.
The vines are used in addition to a clasping of hands to signify a joining in life, love, or business. Any enterprise undertaken by two parties is sealed with th entwining of this 'Eidheann' plant around the clasped arms of the constituents.