The huisache or sweet acacia (Acacia farnesiana (L.) Willdenow) is a small thorny tree in the Mimosa tribe of the Fabaceae, the legume family. There are over 800 species of Acacia in the world; various species are native to Africa, Australia, and the Americas. Sweet acacia is a plant with a mysterious past; it is thought native to warm temperate and tropical America, but the tree is now found on every continent with latitudes between 30 degrees N and 40 degrees S. No one is certain how the sweet acacia spread around the globe. ("Acacia farnesiana (L.) Willd.", John A. Parrotta, USDA Forest Service)

The flowers are arranged in small globular inflorescences. Each flower is only a couple of millimeters; the inflorescence is slightly larger than a centimeter. But the fragrance is tremendous. It was probably the Spanish explorers appreciating the rich warm violet fragrance who first carried seeds back to the Mediterranean. But Portuguese, French, English, and Dutch sailors probably also took seeds home for their gardens. Today, the tree is grown in the south of France, Morocco, Egypt, and Lebanon for the perfume industry.

The extracted essence of sweet acacia is known as cassie absolute. According to The Good Scents Company (2004), the absolute is a dark yellow or pale brown viscous liquid. The essential oil is extracted by emersing the flower heads in refined fats, then distilling to separate the fats from the essence. Cassie absolute is described as "fresh, sweet, spice, clove, violet, green, weedy, woody" and is considered "a valuable and scarce perfume material...." (The Good Scents Company)

Sweet acacia seeds are relished by birds and other wildlife and cattle love the seed pods. The trees readily establish on ruderal (disturbed) soils and are fire tolerant. The trees can burn to the ground and re-sprout from the roots in a matter of days. In some areas of rangeland in Texas and the western states and in Hawaii, the trees become so thick that they are considered a nuisance by ranchers and land managers.