The generic boundaries of Atriplex have long been unclear. Halimione Aell. and Obione Gaertn., both represented in Belgium as natives or aliens, are characterised by hardened, almost completely fused fruiting bracteoles but otherwise scarcely differ from Atriplex s.str. They have often been included in Atriplex by recent authors (see for instance Uotila 2001, van der Meijden 2005, Suchorukow 2007, Stace 2010) but Kadereit & al. (2010) demonstrated that Halimione should be excluded from Atriplex.
The shrubby Atriplex halimus is sometimes planted in the seadunes for erosion control or as a windbreak. It was introduced around 1920 in the dunes between Blankenberge and Zeebrugge and near Knokke and was well-established for some time. It still exists in the coastal dunes in northern France, close to the Belgian frontiers, and could re-appear some day.
An additional species, Atriplex oblongifolia, is recently increasingly found in neighbouring areas, especially along motorways. It superficially resembles native Atriplex patula and might have been overlooked. However, in Atriplex oblongifolia leaves are densely white-mealy beneath and fruiting bracteoles are entire and smooth (see also Gudžinskas & Sukhorukov 2004).
1. Fruiting bracteoles almost entirely fused, becoming very hard. Leaves silvery white === 4. Atriplex sibirica
1. Fruiting bracteoles free to base or fused to above middle, thin and papery or hardening. Leaves green or greenish-white, reddish or rarely more or less silvery === 2
2. Flowers of two kinds: few with horizontal seeds and a perianth of (3-) 5 tepals (bisexual and Chenopodium-like) and many with vertical seeds enclosed by two bracteoles === 3
2. Flowers all alike (with vertical seeds enclosed by a pair of bracteoles) === 4
3. Leaves greenish or reddish, not conspicuously farinose beneath, dull above. Fruiting bracteoles rounded at apex, nearly as broad as long. Main veins of fruiting bracteoles fused above base for ca. 1/5 of the bracteole length === 1. A. hortensis
3. Leaves conspicuously farinose beneath, much paler than above, often more or less shiny. Fruiting bracteoles acute at apex, longer than broad. Main veins of fruiting bracteoles diverging immediately above base === 3. Atriplex sagittata
4. Fruiting bracteoles entirely herbaceous, free to base or fused to middle. Leaf veins not dark-coloured === 5
4. Fruiting bracteoles hardened at base, fused for about half their length. Leaf veins dark-coloured === 6
5. Fruiting bracteoles free to base, entire, thin and almost orbicular, without appendages. Plant often tall (40-150 cm) === 2. A. micrantha
5. Fruiting bracteoles fused at base or up to ½ their length, rhombic or triangular, entire to toothed at margin, often with appendages (native) === A. glabriuscula, A. littoralis, A. patula and A. prostrata
6. Inflorescence a long, leafless terminal panicle. Upper part of bracteoles almost entire. Plant of ruderal habitats === 5. A. tatarica
6. Inflorescence leafy, axillary or is a short terminal panicle. Upper part of bracteoles toothed. Exclusively halophilous (native) === A. laciniata
Additional aliens: Atriplex eardleyae Aell. (Aus., wool alien), A. halimus L. (Medit., garden escape), A. holocarpa F. Muell. s.l. (syn.: A. spongiosa F. Muell., Senniella spongiosa (F. Muell.) Aell.) (Aus., wool alien), A. leptocarpa F. Muell. (Aus., wool alien), A. muelleri Benth. (Aus., wool alien), A. oblongifolia Waldst. et Kit. (E-Eur., W-As., vector unknown), A. pseudocampanulata Aell. (Aus., wool alien), A. rosea L. (S and E-Eur., C-As., wool alien), A. semibaccata R. Brown (Aus., wool alien) and A. suberecta Verdoorn (Aus., wool alien).
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