THE BASES OF ANGIOSPERM PHYLOGENY: CHEMOTAXONOMY1'2 D. E. FAIRBROTHERS3, T. J. MABRY4, R. L. SCOGIN5 AND B. L. TURNER4 ABSTRACT The use of the distribution patterns of plant natural products-alkaloids, terpenes,phenolics, etc.-is well established as a major tool for investigating population structures,species, and phyletic relationships of genera. Here, it is suggested that the distribution pattemsof biogenetically closely related substances should be of considerable value for deducingevolutionary relationships at higher taxonomic levels. Approximately 540 plant taxa (cultivarsthrough orders) have been included in approximately 150 systematic serological publications inthe last 25 years. Research has demonstrated that extracts of seeds, pollen, leaves, tubers, andspores of vascular plants can be used if the required extraction procedures are followed. Bothquantitative and qualitative immunological techniques have provided complementary datawhich have proven to be provocative and valuable in the classification of higher plants. Theexamples presented clearly indicate serology has contributed chemical data which can be-andhave been-used with other data to aid in producing systems of classification such as those ofCronquist and Takhtajan. The phylogenetic relationships among 15 species belonging to12 families of vascular plants based on a comparison of cytochrome c amino acid sequencesagree in general outline with morphologically based phylogenetic diagrams. Amino acidsequence data on homologous plant proteins are in too limited a supply to permit other thanvery preliminary phylogenetic comparisons. Acquisition of more data will require considerabletime and work before an impact will be realized. Published protein sequence data have notrevolutionized presently accepted phylogenetic diagrams, and it is too soon to hint at theultimate contribution of sequence data to phylogenetic schemes. The technique of nucleic acidhybridization is, in principle, applicable to chemotaxonomy at ail taxonomic levels since itinvolves the fundamental hereditary material deoxyribonucleic acid (DNA) and its transcribedcopy, ribonucleic acid (RNA). In contrast to the relative ease with which meaningful plantnatural products distribution patterns are determined, are the difficulties and patience requiredto carry out nucleic acid hybridization experiments and to interpret the results from them.Thus, it is not surprising that few nucleic acid hybridization data for higher plants are availableto meaningfully influence the interpretations of Cronquist and Takhtajan for the evolution ofthe angiosperms; nevertheless, the method inherently has great potential. GENERAL INTRODUCTION With the development of plant natural products chemistry, which deals witha myriad of alkaloids, phenolics, mustard oils, terpenoids, etc., botanists andchemists have revealed that it is possible to employ chemical constituents to helpcharacterize, classify, and describe taxa. Attempts to correlate morphologicaland chemical characteristics are very old. Greene (1909) indicated that the mostremote and primitive of botanical writers, of whatever country, found a botanical 1The Abstract, General Introduction, and Macromolecules-Systematic Serology wereprepared by D. E. Fairbrothers. Micromolecules-Plant Natural Products and Macromolecules-Nucleic Acid Hybridizations were prepared by T. J. Mabry. Macromolecules-Amino AcidSequences was prepared by R. L. Scogin. The General Summary and Conclusions was preparedby B. L. Turner. SPortions of the research were supported by NSF Grant (GB-13202) awarded to D. E.Fairbrothers and NSF Grant (BMS71-01088), NIH Grant (HD-04488), and R. A. WelchFoundation Grant (F-130) awarded to T. J. Mabry. a Department of Botany, Rutgers University, New Brunswick, New Jersey 08903. ' Department of Botany, University of Texas, Austin, Texas 78712. SRancho Santa Ana Botanic Garden, Claremont, California 91711.ANN. MIssouri BOT. GARD. 62: 765-800. 1975.