TORRELL, MONTSERRAT and JOAN VALLčS.* Laboratori de Botānica, Facultat de Farmācia, Universitat de Barcelona, Av. Joan XXIII, s/n, 08028 Barcelona, Catalonia. - Studies on genome evolution in the genus Artemisia L. (Asteraceae, Anthemideae, Artemisiinae).
The genus Artemisia, the largest in the tribe Anthemideae and
one of the larger in the family Asteraceae, comprises around 500 taxa
at specific and subspecific levels, largely distributed in the
temperate regions of Northern Hemisphere. It includes several species
that dominate the landscape in arid and semi-arid areas, as well as
some useful taxa. The currently most accepted infrageneric
classification consists of five big groups (Artemisia, Absinthium,
Dracunculus, Seriphidium and Tridentatae), the limits and
the systematics of which have been controversial. In order to achieve
a natural classification of the genus and a definite idea about its
phylogeny, we undertook the study of its genome at three levels:
cytogenetics, genome size and internal transcribed spacers (ITS) of
nuclear ribosomal DNA sequencing. The major findings of our research
are presented in this contribution. Artemisia chromosomes are
rather small and symmetrical. Dysploidy (two basic numbers, x=9 and
x=8) and polyploidy (ploidy levels ranging from 2x to 12x) are the two
main mechanisms of chromosomal evolution in the genus. Banding
techniques and fluorescent in situ hybridization (FISH) allowed us to
establish some differences between taxa or groups of species. Nuclear
DNA amount shows a seven-fold variation in the genus. Some variations
have systematic implications whereas some others are linked to
ecological selection pressures. ITS sequencing provided a consensus
tree that allows us to confirm the delimitation of the genus,
including Seriphidium, which has been treated as an independent
genus by several authors. Three more big groups (Absinthium,
Dracunculus and Tridentatate) are also well defined,
whereas Artemisia does not appear as a homogeneous group. The
combination of all these data and those from studies that we are
presently carrying out in Artemisia and related genera will
probably throw light on the systematics and the phylogeny of the
entire subtribe Artemisiinae.
Key words: Anthemideae, Artemisia, Asteraceae, cytogenetics, molecular phylogeny, systematics