3. Amaranthus blitum L. (syn.: A. lividus L. p.p., A. ascendens Loisel.) (Medit.) – A rather frequent, locally naturalised and probably increasing alien. Known at least since the first half of the 19th century in Belgium and sometimes claimed as an archaeophyte. Formerly chiefly introduced with wool, more recently usually as a contaminant in cereals or a nursery weed. Nowadays a rather common urban weed in many (larger) cities in plantations, foot of walls and other warm, sun-exposed habitats.
Amaranthus blitum is a variable species and several subspecific taxa have been described some of which are sometimes treated at specific rank (see for instance Hügin 1987). We here tentatively follow Costea & al. (2001b) but the appropriate rank of taxa within Amaranthus blitum surely requires further investigation. Three more or less distinct subspecies are distinguished:
1. Fruit 1,2-1,8 mm diameter. Seeds 0,8-1,1 mm. Leaves often small (rarely exceeding 20 mm), deeply notched at apex === subsp. emarginatus
1. Fruit 1,8-3 mm diameter. Seeds 1,1-1,8 mm. Leaves usually larger, less distinctly notched at apex === 2
2. Leaves large, up to 9 cm long. Seeds smooth, with rounded margins. Bracts with the midvein branched === subsp. oleraceus
2. Leaves smaller. Seeds sculptured, with acute margins. Bracts with the midvein unbranched === subsp. blitum
These subspecies are already recognisable in the plantlet stage (see Costea & al. 2001b for further details) which is uncommon in the genus Amaranthus.
All three subspecies have been recorded in Belgium but their distribution and degree of naturalisation is insufficiently known. Subsp. oleraceus (L.) Costea (syn.: A. oleraceus L., A. blitum var. oleraceus (L.) Hook. f., A. lividus var. lividus, A. lividus subsp. oleraceus (L.) Soó) used to be grown as a vegetable (a substitute for spinach) but is probably extinct as such in Belgium. The two other subspecies, subsp. emarginatus (Moq. ex Uline et Bray) Carretero, Muñoz Garmendia et Pedrol (syn.: A. emarginatus Moq. ex Uline et Bray, A. blitum subsp. polygonoides (Moq.) Carretero, A. lividus subsp. polygonoides (Moq.) Hejný, A. lividus var. polygonoides (Moq.) Thell. ex Druce) and subsp. blitum are still frequently encountered. The usual subspecies in urban areas (pavement and flowerbed weed) and greenhouses seems to be subsp. blitum. Subspecies emarginatus is possibly rarer and, at least partially, confined to harbour areas (for instance near grain mills). In several European countries, this taxon is recently much increasing in riverine habitats and should be looked for on gravelly or sandy riverbanks in Belgium as well. Both subspecies are probably naturalised in Belgium. Subsp. emarginatus is originally confined to subtropical areas but fast spreading in more temperate areas, whereas the more temperate subsp. blitum apparently is decreasing lately (Costea & al. 2001b).
Subspecies emarginatus itself is fairly variable. More or less vigorous plants with larger leaves and a long, thin and flexuous terminal inflorescence are sometimes segregated as var. pseudogracilis (Thell.) Costea (syn. A. emarginatus subsp. pseudogracilis (Thell.) Hügin) (see for instance Hügin 1987, Costea & al. 2001b). Such plants have been recorded in Belgium as well (for instance in Andenne in 1946) and might have been overlooked.
Costea M. (1998) Amaranthus L. subgenus Albersia (Kunth) Gren. & Godr. in Romania. Rev. Rom. Biol. 43: 95-112.
Costea M., Sanders A. & Waines G. (2001b) Notes on some little known Amaranthus taxa (Amaranthaceae) in the United States. Sida 19(4): 975-992.
Hügin G. (1986) Die Verbreitung von Amaranthus-Arten in der südlichen und mittleren Oberrheinebene sowie einigen angrenzenden Gebieten. Phytocoenologia 14: 289-379.
Hügin G. (1987) Einige Bemerkungen zu wenig bekannten Amaranthus-Sippen (Amaranthaceae) Mitteleuropas. Willdenowia 16: 453-478.
Jehlík V. (2005) Amaranthus blitum L. subsp. emarginatus (Moq. ex Uline et W. L. Bray) Carretero, Muñoz Garm. et Pedrol the new invasive subspecies native to the tropics occurs now also in Slovakia and Hungary. Thaizia 15, Supp. 1: 115-120.
Verloove F. (2006) Amaranthus blitum. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 130.