TERPENOIDS 



245 



and the Taxaceae (including Podocarpus), Holloway considered that 

 the distribution of the diterpenes was opposed to this older taxonomic 

 disposition. Sciadopitys, by more recent treatments, is placed in the 

 Taxaceae, but the genus may be somewhat closer to Araucaria, 

 according to Holloway, if one uses certain criteria related to embryo 

 development, gametophyte structure, and fertilization. He does not 

 deny, however, the similarities between Sciadopitys and other genera 

 in the Taxodineae, but he still considers it possible that the genus 

 diverged from the main Araucarian stock at an early time. It would 

 be interesting to know the total distribution of these diterpenes. 



Holloway constructed a diagram to illustrate the relation of 

 the occurrence of the phyllocladene and podocarprene diterpenes and 

 conifer phylogeny (Fig. 13-3). All genera to the right of the Taxineae 

 either have these diterpenes or are postulated to have them. 



As noted in Chapter 14 the genus Podocarpus is biochemically 

 distinctive in that its lignin contains some syringyl derivatives typi- 

 cally absent from the lignins of other conifers. 



A small group of compounds of rather limited distribution on 

 the basis of present knowledge, the tropolones, has been investigated 

 particularly by Erdtman (1955a). Among vascular plants tropolones 

 have been isolated only in the gymnosperms, in fact, only within the 

 Cupressaceae. According to Erdtman (1955b), ". . . the idea that they 



Sciadopitys „ ,. Phyllocladus 



Dacrydium 



Taxodineae 

 Cupressineae 



Abietineae 



Podocarpus 



Pherosphae^^j^^^^^^^^y^ 



Saxegothea 

 Araucaria 



Agothis 



Fig. 13-3. Conjectural diagram of conifers based on diterpene 

 content. All taxa to right of Taxineae postulated to produce diter- 

 penes of phyllocladene or podocarprene (after Holloway, 1958). 



