Arabia: Branch of a myrrh tree (Balsamodendron ehrenbergianum), Amsterdam, 1881

Myrrh is the aromatic oleoresin of a number of small, thorny tree species of the genus Commiphora, which grow in dry, stony soil. An oleoresin is a natural blend of an essential oil and a resin. Myrrh resin is a natural gum. When a tree wound penetrates through the bark and into the sapwood, the tree bleeds a resin. Myrrh gum, like frankincense, is such a resin. When people harvest myrrh, they wound the trees repeatedly to bleed them of the gum. Myrrh gum is waxy, and coagulates quickly. After the harvest, the gum becomes hard and glossy. The gum is yellowish, and may be either clear or opaque. It darkens deeply as it ages, and white streaks emerge. Myrrh gum is commonly harvested from the species Commiphora myrrha, which is native to Yemen, Somalia, and eastern Ethiopia. The related Commiphora gileadensis, native to Eastern Mediterranean and particularly the Arabian Peninsula, is the biblically referenced Balm of Gilead. Several other species yield bdellium, and Indian myrrh. The oleo gum resins of a number of other Commiphora and Balsamodendron species are also used as perfumes, medicines (such as aromatic wound dressings), and incense ingredients. (Photo by: Pictures From History/Universal Images Group via Getty Images)