The Naturalis Historia of Pliny the Elder consists of 37 books, of which 16 are devoted to botany. About 900 plants are named, but many names are synonyms and identification is often impossible. Where identification is possible it is achieved by comparison of the actual names with the vernacular names in related languages or by indirect evidence from their medical use. In this way 130 plants used in renal therapy during Roman times can be identified. Many were eaten as part of the diet, and the distinction between medicinal and edible plants was not clearcut. Pliny was also the first author to comment that wild species are more active than cultivated ones. Most of the plants reported by Pliny are also mentioned by Dioscorides, and more than 30 of them were also listed by Plenck. Several are still quoted in modern pharmacopeias.