Polycyclic isoprenoids are divided into groups based on how many C10 units, or we say terpenoids their precursors possessed. Thus, for example, a triterpane had a precursor that had between 30 and 40 carbons.
- Monoterpenoids, C10
- Diterpenoids, C20
- Triterpenoids, C30 (all synthesized from the same precursor, squalene)
- Tetraterpenoids, C40, which include carotenoids