Cytogenetics of Four Common Shrub Species of the Mexican Xerophile Scrub in the Mezquital Valley, Hidalgo, Mexico

Abstract

Chromosomal characteristics of Dasylirion acrotrichum (Asparagaceae), Flourensia resinosa, (Asteraceae), Tecoma stans (Bignoniaceae), and Citharexylum brachyanthum (Verbenaceae), common elements of the Mexican xerophile scrub are recorded for the first time. The spreading and air-drying technique in root meristems allowed for obtaining chromosome preparations. Chromosomal parameters such as the diploid number (2n), karyotype formula (KF), total haploid chromosome length (THL), average chromosome size (AC), and asymmetry index (TF%) of the analyzed species were obtained, except in C. brachyanthum where neither KF nor TF%. The karyotype formulae of D. acrotrichum (13m+6sm), F. resinosa (11m+7sm), and T. stans (14m+3m+1stsat) represent the first cytogenetic records in Mexican populations. Differences in KF, AC, and position of the satellites concerning other previously analyzed cogenerics show that speciation involves changes in the size and shape of the chromosomes. The diploid numbers confirm basic numbers (x) already recorded, but a 2n=104 observed in C. brachyanthum and the same number in C. myrianthum from Brazil could modify x=9 in favor of x=13, consistent with karyological variation in Verbenaceae where hybridization and polyploidy, among other numerical variation mechanisms, play an important role in chromosomal differentiation. The taxa studied showed satellites in the short arms of chromosomes with displaced centromere. These data are taxonomically useful and could be associated in part with the geographic distribution of the species.