Recent molecular phylogenetic research strongly suggests the inclusion of Chenopodiaceae in Amaranthaceae (APG 1998-2009). This taxonomy became widely accepted in recent times (see for instance van der Meijden 2005, Stace 2010) and is adopted here as well.
Polycnemum L. is only remotely related to most members of Amaranthaceae s.l. and is possibly better segregated (see for instance Kadereit & al. 2003). Polycnemum majus A. Braun is an extinct native species (Lawalrée 1953, Lambinon & al. 2004) and P. arvense L. was last seen an alien in Belgium in 1903 (Verloove 2006). Similarly, Einadia Raf. is here tentatively accepted as a distinct genus (pending additional studies) but it might well a member of Australian Chenopodium (Kadereit & al. 2010).
The generic limits of Chenopodium s.l. and related taxa have considerably changed as a result of recent molecular phylogenetic studies (see Fuentes-Bazan & al. 2012 for an overview). Dysphania R. Br. (for species with aromatic, glandular hairs) had already been segregated before on morphological grounds (Mosyakin & Clemants 2002) and this is confirmed by molecular data. Chenopodium, as traditionally understood, finally turns out to fall apart in six independent lineages and the Belgian representatives (native as well as non-native) should be classified as follows (5 lineages present):
Lipandra Moq. with a single, native species:
L. polysperma (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium polyspermum L.)
Oxybasis Kar. & Kir., with 5 species (4 native, 1 non-native, preceded by an asterisk):
O. chenopodioides (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium chenopodioides (L.) Aellen)
O. glauca (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium glaucum L.)
* O. macrosperma (Hook. f.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium macrospermum Hook. f.)
O. rubra (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium rubrum L.)
O. urbica (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium urbicum L.)
Blitum L., with a single native species and three non-native species (preceded by an asterisk):
Blitum bonus-henricus (L.) Reichenb. (syn.: Chenopodium bonus-henricus L.)
* Blitum capitatum L. (syn.: Chenopodium capitatum (L.) Ambrosi)
* Blitum nuttallianum Schult. (syn.: Monolepis nuttalliana (Schult.) E. Greene)
* Blitum virgatum L. (syn.: Chenopodium foliosum Aschers.)
Dysphania R. Brown, with nine non-native species (preceded by an asterisk):
* D. ambrosioides (L.) Mosyakin et Clemants (syn.: Chenopodium ambrosioides L.)
* D. botrys (L.) Mosyakin et Clemants (syn.: Chenopodium botrys L.)
* D. carinata (R. Brown) Mosyakin et Clemants (syn.: Chenopodium carinatum R. Brown)
* D. cristata (F. Muell.) Mosyakin et Clemants (syn.: Chenopodium cristatum (F. Muell.) F. Muell.)
* D. glomulifera (Nees) P.G. Wilson (syn.: Chenopodium myriocephalum (Benth.) Aellen)
* D. multifida (L.) Mosyakin et Clemants (syn.: Chenopodium multifidum L.)
* D. pseudomultiflora (J. Murr) Verloove et Lambinon (syn.: Chenopodium pseudomultiflorum (J. Murr) Uotila)
* D. pumilio (R. Brown) Mosyakin et Clemants (syn.: Chenopodium pumilio R. Brown)
* D. schraderiana (Schult.) Mosyakin et Clemants (syn.: Chenopodium schraderianum Schult.)
Chenopodiastrum S. Fuentes, Uotila & Borsch, with two native and one non-native species (preceded by an asterisk):
C. hybridum (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium hybridum L.)
C. murale (L.) S. Fuentes, Uotila & Borsch (syn.: Chenopodium murale L.)
* C. simplex (Torrey) S. Fuentes, Uotila & Borsch (syn.: Chenopodium simplex (Torrey) Raf.)
The remaining species belong with Chenopodium s.str. In this new, narrower circumscription it is monophyletic.
In the key beneath this new generic circumscription for Chenopodium and related genera is applied.
1. Leaves scale-like, not developed (i.e. forming succulent sheaths around stem). Stem succulent and jointed, especially when young. Plants confined to saline habitats (native) === Salicornia
1. Leaves not scale-like, well developed. Stem never jointed. Plants of various habitats === 2
2. All leaves opposite. Flowers in axillary whitish heads === Alternanthera
2. Leaves mostly alternate, rarely some or most opposite (in the latter case inflorescences never axillary and whitish) === 3
3. Leaves linear-subulate, (semi-) cylindrical, usually succulent. Plants mostly confined to saline habitats (native) === Salsola and Suaeda
6. Basal rosette usually absent at anthesis. Indumentum often present === 8
7. Rosette leaves usually 20-50 cm long, stem leaves not hastate at base. Flowers bisexual with 5 tepals. Fruit without teeth or spines. Seeds horizontal === Beta
7. Rosette leaves rarely exceeding 20 cm, stem leaves often hastate at base. Flowers unisexual: male in dense spikes or panicles, female axillary. Fruit often with apical teeth or spines. Seeds vertical === Spinacia
8. Female flowers without perianth but enclosed by two accrescent bracts === 9
8. Female flowers with perianth === 10
9. Fruiting bracteoles almost entirely fused, becoming very hard. Silvery or greyish-white subshrubs with leaves with entire margins (native) === Halimione
9. Fruiting bracteoles usually 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 (if exceptionally fruiting bracteoles almost entirely fused and becoming very hard, than annual herb with leaf margins irregularly dentate or with basal lobes) === Atriplex
10. Perianth segments of bisexual flowers transversally winged in fruit. Leaves entire, narrowly lanceolate to almost linear, rarely wider than 5 mm === Bassia
10. Perianth segments not transversally winged (but often with a longitudinal keel!). Leaves either wider or not entire at margin === 11
11. All female flowers with 3-5 bracteoles. Perianth brownish and scarious, often regularly dehiscent at maturity === Amaranthus
11. Bracteoles usually absent or inconspicuous. Perianth usually greenish and herbaceous (sometimes succulent and red) === 12
12. Plant (at least in part) with glandular or glandular-vesicular hairs, aromatic ===Dysphania
12. Plant glabrous or mealy, without glandular hairs, odourless or foetid, not aromatic === 13
13. Inflorescence in loose monochasial or dichasial cymes. Plant always glabrous (native) === Lipandra
13. Inflorescence in loose or dense spikes or panicles. Plant often mealy (farinose), at least when young, or glabrous === 14
14. Stem unbranched or sparingly branched. Perianth often succulent in fruit, with 1-5 segments. Stigmas 2-4. Seeds always vertical. Basal rosette sometimes present === Blitum
14. Stem usually branched. Perianth never succulent in fruit, with 3-5 segments. Stigmas 2. Seeds vertical and/or horizontal. Basal rosette always absent === 15
15. Flowers usually dimorphic, in lateral flowers with 3 perianth segments. Seeds mostly vertical, some horizontal. Stamens 1-3 === Oxybasis
15. Flowers not dimorphic, all with 5 perianth segments. Seeds all horizontal. Stamens always 5 === 16
16. Foliage and stems glabrous or very sparsely mealy (farinose) when young only. Perianth segments with distinct midvein on inner side === Chenopodiastrum
16. Foliage and stems always distinctly mealy (farinose), mostly persistent at maturity. Perianth segments without distinct midvein on inner side === Chenopodium
Additional aliens: Einadia polygonoides (J. Murr) Wilson (syn.: Chenopodium polygonoides (J. Murr) Aellen) (Aus., wool alien), Polycnemum arvense L. (Euras., wool alien), Ptilotus spec. (Aus., wool alien), Sclerolaena muricata (Moq.) Domin (syn.: Anisacantha muricata Moq., Bassia quinquecuspis (F. Muell.) F. Muell., Chenolea quinquecuspis F. Muell.) (Aus., wool alien) and Spirobassia hirsuta (L.) Freitag et Kadereit (syn.: Bassia hirsuta (L.) Aschers., Kochia hirsuta (L.) Nolte) (Euras., vector unknown).
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