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Chromosome Numbers and Their Systematic Significance in Some Mexican Melastomataceae

Frank Almeda and Tsan Iang Chuang
Systematic Botany
Vol. 17, No. 4 (Oct. - Dec., 1992), pp. 583-593
DOI: 10.2307/2419728
Stable URL: http://www.jstor.org/stable/2419728
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Chromosome Numbers and Their Systematic Significance in Some Mexican Melastomataceae
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Abstract

Original meiotic chromosome counts are reported for 35 species and one natural interspecific hybrid in 11 genera of Mexican Melastomataceae. These include first counts for 24 species in three of the nine recognized New World tribes in the family. Counts of n = 18 for Arthrostemma parvifolium and n = 36 for Topobea calycularis represent new numbers for these genera. Other counts for species of Arthrostemma (n = 30), Centradenia (n = 18), Clidemia (n = 17, 23), Conostegia (n = 17), Heterocentron (n = 18), Leandra (n = 17), Miconia (n = 17), Monochaetum (n = 18), Pterolepis (n = 7), and Tibouchina (n = 9, 18) corroborate previously reported numbers for these genera. Centradenia, Heterocentron, and Monochaetum with n = 18 and Conostegia with n = 17 appear to have remarkably constant chromosome numbers, whereas Tibouchina exhibits a polyploid series based on x = 9. Clidemia, Leandra, and Miconia, the largest genera of Miconieae, show greatest variation in chromosome numbers. The widespread occurrence of n = 17 suggests that this is the base number in the Miconieae. Two hypotheses are presented to explain the origin of x = 17 in the Miconieae. One suggests straight autotetraploidization of x = 9 followed by chromosome loss (2x - 1). The allotetraploid hypothesis proposes that x = 17 is of dibasic origin and may have formed by ancient hybridization of species with 7 and 10 or 8 and 9 haploid chromosomes.

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