Artemisia is a complex genus of 522 species (Oberprieler & al. 2007; ca. 400 according to Mabberley 2008) in which specific boundaries are still controversial. Recent molecular studies seem to favour a broad generic concept, i.e. including Absinthium (Mill.) DC., Dracunculus Besser, Seriphidium Besser, etc. (Hayat & al. 2009) but additional research is surely required. Ling & al. (2006), for instance, accepted Seriphidium as a distinct genus for Flora of China. Artemisia is most widely distributed in the northern hemisphere (Eurasia and North America), with only few species in Africa and South America. Some species are native in Belgium as well: Artemisia absinthium L., A. alba Turra, A. campestris subsp. campestris, A. maritima L. and A. vulgaris L. Only the latter is a common and widespread species in Belgium. Artemisia absinthium is usually claimed as a native but it surely is at most an archaeophyte. Even today it much more frequently occurs in strongly anthropogenic habitats and many recent records are definitely non-native (port areas, dumps, etc.). Belgian native populations of Artemisia alba and A. campestris subsp. campestris are marginal. The former is confined to rather few populations on thermophilous rocks in the valley of river Meuse; the latter more often occurs as an alien in man-made habitats (railway yards, coalmine heaps,…). Many species of Artemisia are grown as ornamentals or as culinary herbs (often very aromatic). Several are reputed agricultural or environmental weeds.
In addition to the species treated in detail below few others might have been overlooked (see Cullen 2000 and Jäger & al. 2008 for potential garden escapes). See also Ryves (1984) for a concise overview of non-native representatives of the genus in the British Isles.
There are numerous Belgian records of Artemisia pontica but none since 1949. It was apparently frequently cultivated in the 19th century and locally persisted for some time, for instance in a road verge near Mons (at least between 1946 and 1949), on old city walls in Leuven (1886-1888), border of river Meuse near Herstal (1872-1899), etc.
1. Most or all leaves entire (sometimes some 3-fid at apex) === 2
1. At least the cauline leaves divided === 3
2. Stem and leaves green, almost glabrous. Central flowers functionally male, not setting fruit === Artemisia dracunculus
2. Stem and leaves densely white-woolly. Central flowers bisexual and fertile, setting fruit === A. ludoviciana
3. Annual or biennial, without rootstock or non-flowering shoots === 4
3. Perennial (often small shrubs with woody base), with thick rootstocks and non-flowering shoots === 7
4. Entire plant sericeous with rather dense, appressed hairs === A. sieversiana
4. Plant glabrous === 5
5. Inflorescence a narrow spiciform array, 20-40 mm wide, +/- leafy (or with leaf-like bracts) to apex. Leaves 1-2 pinnately lobed. Plant only slightly aromatic (or not at all) === A. biennis
5. Inflorescence a diffusely branched paniculiform array, 100-200 mm wide, not conspicuously leafy to apex. Leaves (1-)2-3 pinnatisect. Plant very aromatic or only slightly aromatic === 6
6. All leaf segments filiform. Heads 1-2 mm across. Plant scarcely aromatic === A. scoparia
6. Leaf segments of cauline leaves not filiform. Heads 2-3 mm across. Plant very aromatic === A. annua
7. Leaf segments of cauline and basal leaves broad, at least 2 mm wide at base === 8
7. All leaf segments narrow, less than 2 mm wide === 11
8. Entire plant greyish-pubescent, leaves white hairy on both sides. Receptacle pubescent (native) === A. absinthium
8. Plant not greyish-pubescent, leaf surface green and glabrous above. Receptacle glabrous === 9
9. Always strongly rhizomatous. Flowering from end of August onwards (or not at all) === 10
9. Caespitose or weakly rhizomatous. Flowering from July onwards (native) === A. vulgaris
10. Middle cauline leaves pinnatisect, with long (untoothed) apical segment, ca. 30 mm long or longer, glandular punctate or not (glands only visible on leaf upper side and often readily deciduous). Flowering from October onwards (or not at all). Inflorescence a narrow panicle with branches not widely diverging. Heads ca. 2.4-3 mm wide, tubular florets usually at least 10. Plant aromatic === A. verlotiorum
10. Middle cauline leaves pinnatipartite, with shorter apical segment, always without glands. Flowering from the second half of August onwards. Inflorescence a wide panicle with branches diverging at 50° or more. Heads ca. 1.5-2 mm wide, tubular florets always less than 10, usually ca. 5. Plant not or slightly aromatic === A. princeps
11. Receptacle pubescent. Plants from natural habitats (calcareous rocks) (native) === A. alba
11. Receptacle glabrous. Plants from man-made or natural habitats === 12
12. Central florets male === A. campestris s.l.
12. Central florets hermaphrodite, fertile === 13
13. Involucre glabrous. Entire plant glabrous, except for lower side of the leaves. Stems woody for most of their length === A. abrotanum
13. Involucre hairy. Entire plant greyish pubescent. Stems only woody at base === 14
14. Corolla lobes hairy. Outer florets female. Leaves appressed pubescent, more or less sericeous === A. austriaca
14. Corolla lobes glabrous. Outer florets hermaphrodite. Leaves densely tomentose (at least when young), hairs more or less crispate (native) === A. maritima
Additional aliens: Artemisia afra Jacq. (Afr., wool alien) and A. pontica L. (C and E-Eur., SW-As., garden escape).
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