PHENOLIC SUBSTANCES 221 



In summary, phenolics may be regarded as potentially of great 

 systematic importance because of the existence of hundreds of different 

 types, many of which are of restricted distribution. It is probable that 

 a comprehensive review of the chemical, biochemical, and pharmaco- 

 logical literature would establish a number of interesting correlations 

 not already recognized. In most of these cases, additional work would 

 be necessary to substantiate a systematic evaluation. Hegnauer (1956) 

 has reviewed the comparative chemistry of an individual family, the 

 Leguminosae and considered among other groups of compounds, 

 the phenolics. Comprehensive chemical reviews such as that of 

 Karrer (1958), which lists the constitution and occurrence of or- 

 ganic plant constituents, provide insight into attractive possibihties, 

 for example, the distribution of the flavanone, naringenin and other 

 flavanones and their glycosides in the genus Acacia and other mem- 

 bers of the Mimosoideae. Among the commoner phenolics, specific 

 glycoside types are likely to be more significant than the aglycone 

 which have been more often studied. 



Some of the more recently discovered flavonoids, such as the 

 biflavonyls discussed earlier, offer opportunities for phylogenetic in- 

 vestigations. The biflavonyls, for example, are known to occur only 

 in gymnosperms with the exception of Casuarina (Table 11-2). It is 

 notable that biflavonyls are not yet known from Pinaceae, although 

 numerous species have been examined. Baker and Ollis (1961), 

 in noting the presence of biflavonyls in Casuarina stricta, add 

 "This is particularly interesting because of all the angiosperms, 

 Casuarina is the most closely related to the gymnosperms." That this 

 viewpoint is far from unanimous may be quickly ascertained from 

 Lawrence (1951). The more important question is that of how much 

 weight ought to be given to the presence of hinokiflavone, the bi- 

 flavonyl of Casuarina, in linking the group to gymnosperms. 



In contrast to the biflavonyls, another group of recently dis- 

 covered flavonoids, the C-glycosides, thus far have been reported from 

 such widely separated plant groups as the Gramineae, Lemnaceae, 

 Caryophyllaceae, Rosaceae, and Verbenaceae (Horhammer and 

 Wagner, 1961). 



