He developed William’s Triune System of Formulation, which continues to be taught by herbalists, including David Winston, who has significantly expanded LeSassier's materia medica.
[1] LeSassier taught and inspired many of the major herbalists currently practicing in the United States, including Matthew Wood,[2] David Winston, Margi Flint, and Dina Falconi, and his influence is significant.
In the late 1960s, LeSassier opened the Christos School of Herbal Medicine in Taos, New Mexico, where he ran a herb store.
In 1983, he settled in New York City and opened Chiron’s Magic Minerals, where he practiced and taught herbs, bodywork, and energy work.
The back yard of the office was home to many herbs that William grew there including nettles, hops, raspberries, spilanthes, comfrey, holy basel and catnip.
He continued to live in New York, and also spent time in a vacation home in the Blue Ridge Mountains which was also a school and nature preserve.
Herbs in the system are classified by their ability to either build or tonify (+), react amphoterically (which means to stabilize or harmonize) (0), or to eliminate (-).