Culpeper's enduring monument is The English Physitian (1652), later and ever after known as the Complete Herbal. In it he described hundreds of plants, where they grow, how to recognize them, and what ailments they treat, in accessible English aimed at the household rather than the physician's study, so that families could gather and prepare their own remedies from the common plants around them.
What makes the book distinctive, beyond its populism, is its thoroughgoing astrological framework. Culpeper held that every plant, every disease and every part of the body falls under the rulership of a planet, and that healing works by these correspondences, a herb governed by one planet treating an illness governed by its opposite, or strengthening the organ ruled by the same power. This union of herbalism and astrology, drawn from the older doctrine of sympathies and from writers such as the astrologer William Lilly, is the reason his herbal belongs as much to the history of astrology as of botany, and it is why this atlas draws on him among its sources.
The Complete Herbal became one of the most enduring books in the English language, reprinted continuously for more than three centuries and consulted by herbalists to this day, an unusually complete victory for a man who set out to make the specialists' knowledge common property.