Osain is considered to be a "brujo" or witch, because some of the most powerful magic is done working with Osain. Remember that Osain is the owner of all the plants and trees and that includes not only their medicinal uses, but also their magical uses. When we speak of doing witchcraft (brujeria) in the religion, this does not always have a negative connotation. Witchcraft can be done for the benefit of a person. Any magical working in Santeria, whether for good or bad, is called brujeria or witchcraft. It is not like English, where witchcraft has a totally negative interpretation. Osain, as the owner of all the plants and the Master of the Woods, has the power to destroy witchcraft done by brujos or witches, even those working with a "prenda" judia or negative spirits. Osain is greater than all the Prendas of the Mayomberos because Osain controls all the spirits of the different trees that the Prenda spirits work with in performing their magic. That is one of the reasons that Osain is considered to be the "left" hand of the Babalawo, Oddua being the "right" hand. These two Orishas are very important for Babalawos and Oluos to have, so that they have access to forces that can defend them, as well as help those who come seeking help with their problems.
St. Joseph is the Catholic Saint associated with Osain. This probably due to the fact that he has plants in his hands. Even though they are lilies, he is probably the only male Catholic Saint that has plants in his representation. For this reason, the ancestors choose him as the equivalent of Osain. Remember that the ancestors from Cuba generally speaking were basically illiterate. Remember that writing did not exist in West Africa until the colonial period. The Yorubas and the other tribes relied on the passage of knowledge by oral means, since there was no written language until the English and other Europeans made their colonial presence felt.
So naturally, the elders of that time, when looking for a Catholic Saint to represent an Orisha would choose St. Joseph, since the presence of plants in the picture formed an association in their minds with Osain. Many still critizise the use of Catholic pictures and images in Santeria. The pictures and images of themselves have no value, but only serve as a connection to the African Orisha that they represent. This practice not only occurred in Cuba, but also in Brazil, where the Catholic Saints are employed to represent the Orishas as well.
