Cytogeography and chromosome evolution of subgenusTridentataeofArtemisia(Asteraceae)

Abstract

The subgenus Tridentatae of Artemisia (Asteraceae: Anthemideae) is composed of 11 species of various taxonomic and geographic complexities. It is centered on Artemisia tridentata with its three widespread common subspecies and two more geographically confined ones. Meiotic chromosome counts on pollen mother cells and mitotic chromosome counts on root tips were made on 364 populations ( = 3.1 plants per population). These population counts are ∼60% of all Tridentatae counts. Some are first records for taxa. The Tridentatae are a polyploid complex (x = 9) with ploidy levels from 2x to 8x, but mostly 2x (48%) and 4x (46%). Polyploidy occurs in nine of the 11 species and in many subspecies as well. Supernumerary or b chromosomes are present only at a low frequency. In the principal species, A. tridentata, 2x plants are larger than 4x ones, which are adapted to drier conditions, probably in consequence of their slower growth rates. Gigas diploidy is a phenomenon shared by some other woody genera, but is in contrast to the gigas polyploid nature of many herbaceous genera. Polyploidy occurs within populations and is essentially autoploid. Hybridization sometimes occurs at taxa interfaces in stable hybrid zones. Stable Tridentatae hybrid zones coupled with the group's inherent propensity for polyploidization has led to the establishment of a geographically and numerically large and successful complex of species.

Molecular cytogenetic characterization of some representatives of the subgenera <i>Artemisia</i> and <i>Absinthium</i> (genus <i>Artemisia</i>, Asteraceae)

“…The number of B-chromosomes found is also variable, from 1 to 3, when present. The frequency of occurrence of this kind of chromosomes in Artemisia is also a subject of discussion (MCARTHUR & SANDERSON, 1999;GARCIA et al, 2007). Although different kind of B's might be found in plants linked to their origin (VALLÈS & SILJAK-YAKOVLEV, 1997), in A. chamaemelifolia we have only detected some compact, small chromatin bodies, in which the centromere is hardly seen.…”

“…Two different basic chromosome numbers have been described for the genus: x = 9, which is detected in all the subgenera, and the less frequent x = 8, only reported in the subgenera Absinthium, Artemisia and Dracunculus (SOLBRIG, 1977;OLIVA & VALLÈS, 1994;MCARTHUR & SANDERSON, 1999). Both basic chromosome numbers show polyploid series with known levels up to hexadecaploid for x = 9-based species and hexaploid for x = 8 (EHRENDORFER, 1964;PERSSON, 1974;VALLÈS et al, 2001;GARCIA et al, 2006;PELLICER et al, 2007).…”

The Tendency of Chromosomal Evolution in Some Japanese Artemisia using Numerical Analysis of Karyotypes

“…1984, Malakhova 1990, McArthur and Sanderson 1999, Vallès et al 2005, Garcia et al 2006. The most common basic chromosome number of the genus is xϭ9, and less frequent basic number is xϭ8.…”

Deep sequencing of amplicons reveals widespread intraspecific hybridization and multiple origins of polyploidy in big sagebrush (Artemisia tridentata; Asteraceae)

“…However, an understanding of the evolutionary processes involved in the formation of polyploid lineages is often lacking. For many of these shrub taxa, allopolyploidy, autopolyploidy, or a combination of both is believed to play a major role in polyploid formation ( McArthur and Sanderson, 1999 ;Sanderson and Stutz, 2001 ).…”