Amaranthus tuberculatus

18. Amaranthus tuberculatus (Moq.) Sauer (N-Am.) – A rather regular but strictly ephemeral alien since 1983 (see below). Amaranthus tuberculatus is almost exclusively found as a soybean alien in port areas (mainly in Antwerpen and Gent). It is usually found under grain conveyors, near grain mills, on unloading quays or along road verges. Also grown from soybean waste. Recorded once, in 2003, on the gravelly banks of river Maas near Eelen and, similarly, increasingly recorded along rivers Maas and Waal in the Netherlands as well (van der Meijden & al. 2003, van der Meijden & Holverda 2006). In similar habitats Amaranthus tuberculatus (incl. A. rudis; see below) is naturalised in parts of Europe, for instance along river Po in northern Italy (Soldano 1982, Zanotti 1989).

Pratt & Clark (2001) demonstrated that Amaranthus rudis Sauer and A. tuberculatus should be considered as conspecific since they exhibit a continuum of geographic variation. Mosyakin & Robertson (2003) subsequently confirmed the inclusion of Amaranthus rudis in A. tuberculatus. However, Costea & Tardif (2003) suggest their recognition at varietal rank (as var. rudis (Sauer) Costea et Tardif).

Both Amaranthus rudis (sub A. tamariscinus auct. non Nutt.) and A. tuberculatus have convincingly been recorded in Belgium since 1983 (Verloove & Vandenberghe 1993, Verloove 2006). Their identification in Belgium usually is straightforward and their separation is therefore maintained here (see also Costea & al. 2005).

  • Utricle dehiscent. Tepals of female flowers 1-2, lanceolate or linear === var. rudis
  • Utricle indehiscent. Female flowers without tepals === var. tuberculatus

An additional species, Amaranthus australis (A. Gray) Sauer, is very similar to A. tuberculatus (especially var. tuberculatus) but it is non-weedy and not likely to occur as an alien.

Herbarium specimen 1

Herbarium specimen 2


Selected literature:

Costea M. (1997b) Amaranthus tamariscinus Nutt. and Amaranthus palmeri S. Watson in Romania. Acta Horti Buc. 1995-1996: 121-125.

Costea M. & Tardif F.J. (2003) Conspectus and notes on the genus Amaranthus in Canada. Rhodora 105: 260-281.

Mosyakin S.L. & Robertson K.R. (2003) Amaranthus. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 4. Oxford University Press, New York-Oxford: 410-435.

Pratt D.B. & Clark L.G. (2001) Amaranthus rudis and A. tuberculatus – one species or two? J. Torrey Bot. Soc. 128(3): 282-296.

Soldano A. (1982) Naturalizzazione in val Padana di « Amaranthus rudis » Sauer (Amaranthaceae) esotica nuova per la flora italiana. Segnalazione di altre specie di importazione nuove per alcune regioni dell’Italia settentrionale o per qualche provincia del Piemonte. Riv. Piem. St. Nat. 3: 61-70.

Van der Meijden R., Holverda W., van Moorsel R. & van der Slikke W. (2003) Nieuwe vondsten van zeldzame planten in 2001 en 2002. Gorteria 29: 134-154.

Van der Meijden R. & Holverda W. (2006) Nieuwe vondsten van zeldzame planten in 2003 en 2004. Gorteria 32: 1-33.

Verloove F. & Vandenberghe C. (1993) Nieuwe en interessante graanadventieven voor de Noordvlaamse en Noordfranse flora, hoofdzakelijk in 1992. Dumortiera 53-54: 35-57.

Waselkov K.E. & Olsen K.M. (2014) Population genetics and origin of the native North American agricultural weed waterhemp (Amaranthus tuberculatus; Amaranthaceae). Am. J. Bot. 101(10): 1726-1736. [available online at:]

Zanotti E. (1989) Segnalazioni di Amaranthus rudis Sauer e Amaranthus bouchonii Thell. in alcune località delle province di Bergamo, Brescia e Cremona. Pianura 3: 47-54.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith