Artemisia Systematics and Phylogeny: Cytogenetic and Molecular Insights

The genus Artemisia (Asteraceae, Anthemideae, Artemisiinae) is a large genus, one of the largest genera in its family. It is comprised of about 500 taxa at the specific or subspecific level, distributed in 5 sections or subgenera. Most species are perennial and many are landscape dominants of arid or semiarid regions. Artemisia is widely distributed in the Northern Hemisphere but poorly represented in the Southern Hemisphere. It is more richly represented in Eurasia than it is in North America. A number of Artemisia species have a high economic value for food, medicine, forage, ornamentals, and other uses. Some taxa are invasive weeds, which can adversely affect harvests. Even though some features (carpological and palynological ones) are quite constant and characteristic of the genus, a high degree of morphological variation exists. Artemisia has two basic chromosome numbers, with ploidy levels ranging from diploid to dodecaploid for x = 9 and from diploid to hexaploid for x = 8. Polyploidy and dysploidy are two very relevant evolutionary mechanisms in the genus, particularly the first one, which is present in all its major groups. The classical systematics of Artemisia have been refined by molecular methods, for example, internal transcribed spacer (ITS) sequences of nuclear ribosomal DNA, chloroplast DNA restriction site (cpDNA) data, and randomly amplified polymorphic DNA (RAPD) analysis but in the main hold well. This presentation provides a general introduction and characterization of Artemisia with particular emphasis on its systematics and evolution as illuminated by cytogenetic and molecular data. Introduction ____________________ Artemisia, one of the larger genera in the family Asteraceae and the largest genus in the tribe Anthemideae, comprises from 200 to more than 500 taxa at the specific or subspecific level (depending on the authors, for example, Bremer and Humphries 1993; Ling 1991a,b, 1995a,b; Mabberley 1990; McArthur 1979), which are distributed in 5 sections or subgenera (Torrell and others 1999b). Many Artemisia species have a high economic value in several fields. Some examples are as food plants (absinth–A. absinthium–and other taxa, such as A. genipi, used in preparation of liquors); as spices (tarragon or estragon–A. dracunculus); in medicine, as an antihelminthic (A. santonicum and related taxa) and a new promising source of anti-malaria biochemicals (A. annua); as forage (A. herba-alba and related species in African and Asian steppes and semideserts and A. tridentata and its allies in North American shrublands); as ornamentals (A. absinthium, A. caucasica, and A. stelleriana among many others); and as soil stabilizing agents in badly disturbed habitats, for example, highways, railroads, and mines (A. ludoviciana and A. vulgaris)—see Bailey Hortorium Staff (1976) and Turner and Wassen (1999) for general reference. On the other hand, some taxa, such as A. verlotiorum, are invasive weeds, which can adversely affect harvests. Some others may be toxic (A. absinthium, for instance) or causative of pollen-induced allergies (the Iberian endemic A. barrelieri among others; Giner and others 1999). Marco and Barberá (1990) give a conspectus of the chemical composition of Artemisia, and revisions of applied aspects of the genus can be found in Pareto (1985) and Tan and others (1998). The high number of taxa, the dominance of some of them in landscapes, and the usefulness of many of them have attracted the interest of the researchers, who have produced a considerable amount of literature concerning Artemisia in many disparate fields of study (systematics in all its approaches, ecology, chemistry, pharmacology, and so forth). This paper provides a general review of different systematic and evolutionary aspects of the genus, with special emphasis on cytogenetic and molecular data. Life Form and Morphology ________ Artemisia species are most commonly shrubs, rarely perennial herbs and more rarely annual or biennial herbs. Thus, perennial plants largely dominate the genus; only 5 percent of the taxa (approximately 10 species) are annual or biennial species. Leaves are alternate or sparse, usually more or less divided (exceptionally entire, such as in A. dracunculus and A. cana), with extremely variable shapes and dimensions. Flower heads are small, basically ovoid, cylindrical or hemispheric in shape, constituted by a rather small number (4–40) of flosculose florets (lacking ligulate ones), and grouped in racemose or paniculate synflorescences. Fruits are pappus-lacking achenes or cypselas, characteristic of the genus (Korobkov 1981; Ouyahya and Viano 1985, 1990; Persson 1974; Vallès and Seoane 1992). Palynological characters are useful markers for the genus Artemisia. The weak (verrucose) exine ornamentation contrasts with the higher (spinulose) one of the other members of the tribe Anthemideae, as already pointed out by Wodehouse (1926) and confirmed by later authors (Dimon 1971; Vallès and others 1987). Some of the morphological traits of Artemisia (non-opposite leaves, absence of radial florets, non-paleate head receptacle, many capitula with few florets in each