Rebernig, Carolin A , Schneeweiss, Hanna , Blöch, Cordula , Obermayer, Renate , Villasenor, Jose Luis , Stuessy, Tod F. .
Phylogeography in Melampodium cinereum (Asteraceae, Heliantheae) of south Texas and adjacent Mexico.
The genus Melampodium (Heliantheae, Asteraceae) comprises 39 species distributed throughout Mexico, Central America and the southwestern U.S.A. Three shrubby xerophytic species on the northernmost edge of the distributional range have white rays: M. leucanthum, M. cinereum, and M. argophyllum. Melampodium leucanthum and M. cinereum have diploid and tetraploid cyto-races, whereas M. argophyllum is known to be only hexaploid. This study focuses on the infraspecific relationships within M. cinereum, which, based on morphological characters has been divided into three varieties: var. cinereum, var. hirtellum, and var. ramosissimum. Infraspecific relationships were studied using AFLP fingerprint data, chloroplast haplotype analysis, and ploidy level estimations (with flow cytometry) to: (1) test if current taxonomic groupings correlate with genetic entities; (2) investigate origin of the polyploids (via allo- or autopolyploidy); (3) determine whether polyploidization occurred once or repeatedly; and (4) explore biogeographic origins of the complex. AFLP data clearly support separation of the varieties into different genetic entities, even though not fully reflecting previous taxonomic concepts based on morphology. Melampodium cinereum var. hirtellum is divided into eastern and western groups, with the former clustering with M. cinereum var. cinereum and the latter with var. ramosissimum. cpDNA analysis with 77 individuals (3 individuals per population) analyzed with four primer combinations (psbA-trnH, ndhF-rpL32r, rpL32f-trnL, trnQ-rps16; 2702 bp) resulted in 54 different haplotypes. This high variation in the chloroplast genome may reflect ancient polymorphisms, having been largely maintained during subsequent range expansion and varietal divergence. It is hypothesized that M. cinereum evolved out of peripheral populations of M. leucanthum in low mountains of northeastern Mexico. Further dispersal northeastward led to divergence now recognized as taxonomic varieties. Tetraploidy developed within the easternmost populations of M. cinereum var. cinereum. Hybridization between M. cinereum and M. leucanthum led to the allohexaploid origin of M. argophyllum.
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1 - University of Vienna, Systematic and Evolutionary Botany, Rennweg 14, Vienna, A-1030, Austria
2 - University of Vienna, Department of Systematic and Evolutionary Botany, Rennweg 14, Vienna, Wien, A-1030, Austria
3 - University of Vienna, Systematic and Evolutionary Botany, Rennweg 14, Vienna, Wien, A-1030, Austria
4 - Universidad Nacional Autonoma de Mexico, Herbario Nacional, Apdo. Postal 70-367, Mexico, D.F., 04510, Mexico
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 28th, 2008
Time: 1:15 PM