Enquiry into Plants and De Causis Plantarum by Theophrastus (ca. 370-ca. 285 BC) are a counterpart to Aristotle's zoological work and the most important botanical work of antiquity now extant. In the former Theophrastus classifies and describes. His On Odours and Weather Signs are minor treatises.

Theophrastus of Eresus in Lesbos, born about 370 BC, is the author of the most important botanical works that have survived from classical antiquity. He was in turn student, collaborator, and successor of Aristotle. Like his predecessor he was interested in all aspects of human knowledge and experience, especially natural science. His writings on plants form a counterpart to Aristotle's zoological works. In the "Enquiry into Plants" Theophrastus classifies and describes varieties- covering trees, plants of particular regions, shrubs, herbaceous plants, and cereals; in the last of the nine books he focuses on plant juices and medicinal properties of herbs. The Loeb Classical Library edition is in two volumes; the second contains two additional treatises: "On Odours" and "Weather Signs." In "De Causis Plantarum" Theophrastus turns to plant physiology. Books One and Two are concerned with generation, sprouting, flowering and fruiting, and the effects of climate. In Books Three and Four Theophrastus studies cultivation and agricultural methods. In Books Five and Six he discusses plant breeding; diseases and other causes of death; and distinctive flavours and odours. Theophrastus' celebrated "Characters" is of a quite different nature. This collection of descriptive sketches is the earliest known character-writing and a striking reflection of contemporary life.