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|Title:||Systematics and Biogeography of South American Tripsacum|
|Author(s):||Fletcher, Gilbert Boughton|
|Department / Program:||Plant Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Distribution patterns of the New World Andropogoneae genus Tripsacum (Gramineae) were studied in an effort to trace its origin and evolution. The genus is widely distributed from about 42(DEGREES)N to 24(DEGREES)S latitude in the Americas and islands of the Caribbean. The largest concentration of species occurs in Meso-America, with ten species mostly confined to south-central Mexico and adjacent Guatemala. Three species are restricted to South America. One species occurs in western Mexico and southern Arizona, and one species extends across the range of the genus. When the worldwide distribution of the Andropogoneae is plotted on a map of the continents as they are assumed to have been positioned during the Cretaceous period, a pattern of decreasing generic and specific densities that radiates from present day India as a center becomes evident. Within the Andropogoneae polyploidy shows a similar pattern, with diploids more common in the Indian subcontinent and polyploids increasing outward, suggesting a migration of the Andropogoneae out of this assumed center of origin. Since Tripsacum is absent from the Old World, the progenitor of this genus probably migrated to the New World (central Mexico) across Africa some 80 million years ago.
The most common South American taxon is T. dactyloides (L.) L. var. meridonale de Wet and Timothy (2n = 36). Closely related to T. dactyloides, but usually occupying more seasonally moist and dry habitats, is T. australe Cutler and Anderson. Smaller plants, with essentially erect culms and leaf sheaths on the culms hirsute rather than tomentose, are recognized as T. australe var. hirsutum de Wet and Timothy. Tripsacum cundinamarce de Wet and Timothy (2n = 36) is a robust species with glaucus leaves. Tripsacum peruvianum de Wet and Timothy is a gametophytic apomict with 2n = 72, 90 or 108 chromosomes. The cultivated Guatemala grass, T. andersonii Gray, occurs spontaneously in the mountains of Venezuela, Colombia, and Peru.
Tripsacum andersonii is characterized by 2n = 64 chromosomes, while other species of Tripsacum are diploid (2n = 36), tetraploid (2n = 72) or rarely triploid (2n = 54), pentaploid (2n = 90) or hexaploid (2n = 108) based on a haploid chromosome number of n = 18. Cytological studies among cytological races of Tripsacum species, and among T. andersonii and hybrids between Tripsacum and Zea reveal that T. andersonii combines a triploid Tripsacum genome (54 chromosomes) and haploid Zea genome (10 chromosomes). Comparative morphology suggests that T. australe or the Meso-American diploids T. latifolium Hitchc., T. laxum Nash or T. maizar Hern. and Randolph contributed to the Tripsacum genome. Distribution of leaf flavonoids seems to exclude T. latifolium as a possible parent, although it typically has a stoloniferous growth habit, a characteristic that is rare in Tripsacum but also typical of T. andersonii.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-14|