A number of herbaceous plants accumulate long-chain hydrocarbons (terpenes) par­ticularly those in the Euphorbiaceae such as the annuals Hevea brasiliensis, Euphorbia lathyris (3-10 t dry weight/ha/year) and Calotropis procera (10.8-21.9 t dry weight/ ha/year). The hydrocarbons are produced, as latex, which consists largely of long — chain C 30 triterpenoids which can be cracked (pyrolysis) to form petrol and diesel. These herbaceous plants can be grown in various parts of the world and give quite good yields in terms of dry weights per hectare. Trees like Eucalyptus globus, Pittosporum resiniferum and Copaifera multijuga also produce oils, often in the fruit as in P. resiniferum, which can also be converted into petrol and diesel. However, with the Brazilian tree C. multijuga, the trunk can be tapped and the oil used directly as a diesel replacement.

Microalgal Hydrocarbons

A small number of algae are capable of producing terpenoid oils, one of which is Botrycoccus braunii, which is reported to accumulate up to 86% dry weight as oil (Dote et al., 1993). Hydrocracking of the oil yielded 62% petroleum, 15% aviation fuel, 15% diesel and 3% heavy oil. The large-scale cultivation of this alga is under development.