164 BIOCHEMICAL SYSTEMATICS 



Mothes and Romeike (1958) have summarized the major dis- 

 tribution of alkaloid types among orders and families of higher plants. 

 Table 9-1 is adapted from their data. In a few places suggestive cor- 

 relations in alkaloid content exist between certain families (or even 

 groups of families as in the isoquinohne types). While certain of these 

 correlations will be discussed in this chapter, in general the meaning 

 of such data is not yet sufficiently clear, and the known biosynthetic 

 relationships are too inadequate to allow meaningful speculation. The 

 present writers believe that the diversity of alkaloid types, their com- 

 plexity, and their wide distribution allow much optimism regarding 

 their systematic importance. The taxonomic value of alkaloids is not 

 necessarily restricted to simple correlations of distribution, but later 

 on the basis of studies of comparative biosynthesis, enzymology, and 

 genetic mechanisms, these compounds may yield even more substantial 

 insight into phylogenetic problems. 



Some general considerations of 

 alkaloid distribution and physiology 



It was noted above that alkaloids are rare in animals and in 

 lower plants. Among the former organisms alkaloids are found in such 

 widely separate groups as sea snails (Echinodermata), sand worms 

 (Annelida), toads^, and sharks (Chordata). Alkaloids are apparently 

 absent from algae, mosses, and liverworts, most fungi, and are rare 

 among the simpler vascular plants. For example, only protoalkaloids 

 or other relatively simple alkaloids occur in the divisions Sphenopsida 

 and Lycopsida; alkaloids are unreported from ferns, unreported from 

 cycads, and rare in gymnosperms in general. Thus, other than among 

 flowering plants alkaloids are not widely distributed. Willaman and 

 Schubert (1952) reported that about ninety-seven of the approximately 

 300 angiosperm families were known to have alkaloid-containing 

 genera. Cromwell (1955) stated that forty families of flowering plants 

 contained alkaloids. The reason for this discrepancy is not clear. 

 Surveys of the flora of various regions provide some information 

 about the actual percentage of alkaloid-containing species. A survey 

 of Russian species (Orechov, 1955) yielded 10 per cent, and Australian 

 species (Webb, 1949), yielded 20 per cent alkaloid-containing species. 



3 Toads (Bufo) are notable in that secretions from their parotoid glands contain 

 not only alkaloids [bufotenines, also found in the plant, Piptadenia falcata (Giesbrecht, 

 I960)], but represent the only known vertebrate source of the plant sterol, phytosterol, 

 and also contain bufagins which are similar to the cardiac aglycones found in certain 

 plants. To our knowledge no proposal to include Bufo in the plant order Ranales has yet 

 appeared, even in a chemical journal. 



