It was believed by some ancient civilisations that the Creator has placed his seal on plants to indicate their medicinal use. Nicholas Culpeper was an outstanding advocate. The seeds of Skullcap (headache) resemble tiny skulls; Lungwort has white spotted leaves relative to the tubercula lung; Garlic, with its hollow stalk, relates to the windpipe; White Willow growing in damp places was believed good for rheumatic disorders (it was from the bark of this tree that aspirin was first isolated). Examples are numerous. It is a curiosity that many liver remedies have yellow flowers, those for the nerves (blue), for the spleen (orange), for the bones (white). Serpentaria (Rauwolfia) resembles a snake and is an old traditional remedy for snake-bite.
Herbalism confirms the Doctrine of Signatures but is not based on it.