Monograph of the Lupinus aschenbornii Schauer Complex of the central highlands of Mexico

"Lupinus is a large and taxonomically complex genus of legumes. There are few other genera which have been the subject of so much confusion and misunderstanding. Although much work has been done on the lupines of the U.S. and Canada, the Mexican and South American species are poorly understood. This thesis reports some of the work done on a complex of lupines found in the central highlands of Mexico. The L. aschenbornii Schauer Complex contains several species related by floral and vegetative features. They are all caespitose or subfrutescent perennials with hollow or fistulose stems. The banner in these species is about 9-13 mm long and generally obovate in shape. They are found in pine-oak forests, subalpine pine-fir forests or in alpine meadows on the highest peaks in Mexico. Because so little work has been done on the Mexican lupines, the history of lupine collecting, systematics, distribution and associated geography are reviewed. The geological evolution of Middle America is discussed because of the possible relationships which may exist between some Mexican and South American lupines. An attempt is made to cover the geography, climates and vegetation types associated with Mexican lupines. This review provides a general background for understanding the relationships between the various Mexican species, although more taxonomic work is needed to fully understand these other taxa. The environment of the L. aschenbornii complex is given the most emphasis, particularly the unique subalpine-alpine habitats found near the summits of Mexico's giant volcanos. Since the species of Lupinus are frequently very difficult to separate using morphological features, the potential value of chemotaxonomic methods is explored. Chemical methods have been successfully used with many groups of plants and provide taxonomists with another dimension of characters on which to base taxonomic and phylogenetic decisions. The alkaloids of Lupinus have been much studied in the past and have provided information for taxonomic comparisons. Flavonoids in Lupinus have not recieved as much attention, but appear to have much potential for future investigations. A review of the biosynthetic origins, chemical ecology and taxonomic utility of these compounds is presented to provide a basis for interpreting the results of this study and to update earlier treatments. In addition to a detailed review of the literature, this study utilized a variety of field, laboratory and herbarium techniques. A field trip to Mexico was undertaken to study the habitats of Mexican lupines and to collect specimens. Type descriptions and previous treatments were translated and evaluated. All available herbarium specimens of members of this complex were carefully studied and measured. Floral dissections of these specimens were made to study the flower parts in detail. Chromatographic techniques were used to study the alkaloids and leaf flavonoids found in the complex and comparisons were made with species in other complexes. Various techniqµes used in the study of flavonoids were explored and a procedure developed for using these compounds in the study of lupine taxonomy. The results of this study are incorporated in a taxonomic key and detailed descriptions of the L. aschenbornii Complex. It is hoped that the integration of these approaches results in a more accurate classification and better understanding of the complex, as well as of Mexican lupines in general."--Introduction.