Abstract: Caldesia grandis is a rare and endangered aquatic plant of the Alismataceae
family. This paper first reports 43 chemical components of C. grandis based on the gas
chromatography-mass spectrometry and reviews research on the chemical compositions of
some closely related genera such as Alisma, Sagittaria, and Echinodorus. Their common
chemical components are diterpenoids. Kaurane diterpenoids are found in Caldesia, Alisma
and Sagittaria; clerodane diterpenoids in Sagittaria and Echinodorus; and pimarene and
abietene diterpenoids in Sagittaria. By the biogenesis of diterpenoids, kaurane and abietene
diterpenoids represent evolutionarily derived compounds, clerodane diterpenoids are
primordial, and pimarene diterpenoids are intermediate. The chemotaxonomy, karyotypical
analysis and fossil records of those genera showed that Caldesia was evolutionarily closer to
Alisma than to Sagittaria and Echinodorus. Possible evolution levels of Echinodorus,
Sagittaria, Alisma, Caldesia in chronological order are derived.

Key words: Caldesia grandis, Alisma, Sagittaria, Echinodorus, diterpenoid