^ - BIOCHEMICAL SYSTEMATICS 



34 



made at the family level and lower. Carefully constructed phylogenetic 

 systems have been prepared for numerous generic groups, but only in a 

 few instances (for example, Baker and Smith, 1920, on Eucalyptus) has 

 there been any concentrated effort to evaluate such systems with 

 purely biochemical data. For example, detailed chemotaxonomic work 

 of this nature on the phylogenetic groupings proposed within the 

 genus Crepis (Babcock, 1947) should prove exceedingly rewarding, 

 and might provide new data for relationships yet undetected. The 

 hypothetical phyletic diagram for the genus Hymenopappus (Fig. 2-2) 

 could be used profitably for the orientation of a purely chemotax- 

 onomic study; for example, will biochemical data further support the 

 basic dichotomy indicated by the Series Biennis and Perennis, or 

 will new data come to Hght that might indicate a much more reticulate 

 relationship between the species of these two series than is indicated? 

 It might even be possible to test by chemical data the vahdity of some 

 of the time speculation indicated in the Hymenopappus diagram. For 

 example, it has been demonstrated in numerous instances that certain 

 molecular configurations must occur before some more "advanced" 

 reaction is possible (cf. Ch. 11, p. 197, rotenones). If the latter molecular 

 configuration was found only in the morphologically more advanced 

 desert species, then this would correlate with the evidence from both 

 morphology and paleobotany as to the time of origin of desert habitats 

 and the plant types which must have become adapted to such regions 

 after or concomitant with their development. By the same reasoning, 

 species which have retained certain hypothetical ancestral morpholog- 

 ical features and ecological associations might be shown to have one 

 or several of the metabolic precursors necessary for the molecular 

 advancement indicated. 



The approach to systematics of genera and lower categories 

 using biochemical patterns has not been vigorously pursued, but 

 as indicated by Alston and Turner (1962) it is capable of sufficient 

 refinement that not only are species detectable but also degrees of 

 hybridity for individuals from hybridized populations. Furthermore, 

 it appears likely that with appropriate controls biochemical patterns 

 can be constructed which permit rather objectively determined visual 

 presentation of numerous chemical features for inter- and intra- 

 populational comparisons. Data obtained chromatographically can 

 also be expressed mathematically with a minimum of interpretative 

 effort so that considerable exactness in the presentation of relationship 

 data can be achieved. Limitations involved in this type of comparison 

 are obvious, of course, and further discussion will be devoted to eval- 

 uation of biochemical data in a later chapter. 



The present categorization of vascular plants was developed 



