Abstract
Andropogon is a pantropical grass genus comprising 100–120 species and found mainly in the grasslands of Africa and the Americas. In the new world the genus is represented by approximately sixty (diploids or hexaploids) species grouped in three sections. The hexaploid condition occurs only in the Americas and the full process of this origin is still uncertain, although cytogenetic analysis coupled with taxonomic evidence have provided strong support for new hypothesis. Stebbins proposed the first hypothesis suggesting that the origin of polyploidy in species of Andropogon in North America resulted from duplication of the genome of some diploid species, and then by intergeneric crosses with species of a related genus. Since then, numerous studies were performed to clarify the evolutionary history of the genus in America. In this paper, we present a review of cytogenetic studies in the American Andropogon species during the last four decades.
Highlights
Andropogon L. is a pantropical genus of grasses estimated to contain 100 [1] to 120 [2] species, distributed mainly in the grasslands of Africa and the Americas
Stebbins [8] suggested that the polyploid origin of A. gerardii in North America could be caused by polyploidization of some diploid of the “Cotton Belt” region, resulting in the constitution of the tetraploid A. ternarius, and by intergeneric crosses of this tetraploid with species of Bothriochloa, which at that time were still regarded as members of Andropogon, sect
Nine of them belong to the A. virginicus complex (Table 1), and the other three species are distributed in South and Central America: A. leucostachyus Kunth, A. macrothrix Trin., and A. selloanus (Hack.) Hack
Summary
Andropogon L. is a pantropical genus of grasses estimated to contain 100 [1] to 120 [2] species, distributed mainly in the grasslands of Africa and the Americas. Stapf [4] proposed four sections in the genus for African’s species: (1) Andropogon Stapf, (2) Leptopogon Stapf, (3) Notosolen Stapf, and (4) Piestium Stapf. Genetic differences between American and African (and within) species are poorly understood. Chromosomal evolution, such as polyploidy, appears to be more extensive in America, as hexaploids are almost entirely restricted to this continent (and especially to South America). A. campii Swalen A. canaliglumis Norrmann, Swenson and Caponio A. carinatus Nees A. cordatus Swallen A. crassus Sohns A. crispifolius Guala and Filgueiras A. cubensis Hack. A. ternarius var cabanisii (Hack) Fernald and Griscom A. ternatus (Spreng.) Nees A. tracyi Nash.
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