1 70 BIOCHEMICAL SYSTEMATICS 



While the theoretical position of Wenkert is no doubt sound, 

 the fact is that the most "primitive" known alkaloid-containing plants 

 are vascular plants. These plants also produce carotenoids and lignin. 

 The mevalonate and prephenate pathways were undoubtedly well 

 represented among lower forms possibly hundreds of millions of years 

 before alkaloids appeared. The genetic complexity of a given alkaloid 

 is perhaps best represented by the extent of deviation of the alkaloid 

 from an already established basic metabolic pathway. The reasons for 

 assuming that non-acetate pathways are more likely to involve 

 enzymatically difficult and circuitous routes may be valid, but they 

 are not obvious to the present writers. 



Specific examples of alkaloids of 

 systematic significance 



Alkaloids of the isoquinoline class are probably among the 

 best examples to illustrate the application of biochemical criteria to 

 phylogeny of the higher categories. In this case the disposition of 

 families and perhaps even the proper delimitation of orders are in- 

 volved. Nevertheless, so far the alkaloid chemistry has failed to clarify 

 the taxonomic problems among the groups of plants concerned. 



The isoquinolines, as noted above, are likely offshoots of 

 aromatic amino acid metabolism. Hegnauer (1952, 1954, 1958) has 

 discussed the taxonomic distribution of the entire group of related 

 alkaloids, and our treatment is derived principally from his compre- 

 hensive account. A partial list of families containing isoquinolines 

 follows. For later reference purposes the list is divided into the 

 categories of Lignosae and Herbaceae (Hutchinson 1959). 



The families hsted above are recognizable as representing in 

 general rather "primitive" families by Hutchinson's criteria, and 

 except for the Aristolochiaceae, Rutaceae, and Papaveraceae, they 

 represent the Ranales of Engler and Diels. Other Ranalian famihes 



