13. Amaranthus powellii S. Watson (N-Am.) – A rather frequent alien from the Amaranthus hybridus complex. Two distinct subspecies are distinguished in Belgium. They are treated in detail below:
- Utricle indehiscent or very irregularly dehiscent. Inflorescence usually with many lateral branches, often not strictly erect and stiff === subsp. bouchonii
- Utricle regularly dehiscent. Inflorescence unbranched or with few widely spaced long branches, stiff and strictly erect === subsp. powellii
An additional taxon, subsp. cacciatoi (Aellen ex Cacciato) Iamonico (syn.: A. bouchonii var. cacciatoi Aellen ex Cacciato), might have been overlooked (Iamonico 2012). It combines the inflorescence shape of subsp. bouchonii with the regularly dehiscent utricles of subsp. powellii. It is only known from the surroundings of Rome so far.
Subsp. bouchonii (Thell.) Costea et Carretero (syn.: A. bouchonii Thell., A. hybridus subsp. bouchonii (Thell.) O. Bolós et Vigo, A. hybridus var. bouchonii (Thell.) Lambinon) (N-Am.) – A frequently naturalised and increasing alien, known at least since 1957 but still insufficiently known. Most widespread in Flanders, especially as an agricultural weed (chiefly in maize fields). Also a fairly frequent grain alien in port areas or by railway tracks (Bruynseels & al. 1983), but in such habitats often merely ephemeral.
According to Costea & al. (2001a) subsp. powellii is the usual agricultural and segetal weed in Europe whereas subsp. bouchonii primarily occurs as a pioneer on riverbanks. This apparently does not apply (yet) to the Belgian situation although subsp. bouchonii indeed is increasingly found on gravelly banks of river Maas (found for instance in abundance in 2003 near Uikhoven).
The exact origin of this taxon remains obscure. It possibly arose in Europe from an American taxon but currently exists in North America as well. However, it seems that in North America, the situation with indehiscent-fruited forms is much more complicated than in Europe, and that multiple entities may be involved, including deviate forms of Amaranthus powellii s.str. and hybrids of dioecious taxa with species from the A. hybridus-complex (Mosyakin & Robertson 2003).
The indehiscence of the utricle and the rather lax, not stiffly erect inflorescence are characteristic of subsp. bouchonii but less typical plants are sometimes encountered in Belgium as well. Especially the dehiscence of utricles seems to be variable and (irregularly) dehiscent and indehiscent utricles are sometimes found on the same plant. Therefore, this taxon surely not deserves specific rank.
Selected literature: Aellen (1970), Duvigneaud & Lambinon (1976), Bruynseels & al. (1983), Zanotti (1989), Gaffney (1991), Wilkin (1992), Dirkse & al. (1998), Duistermaat (1999), Costea & al. (2001a), Verloove (2002), Mosyakin & Robertson (2003), Verloove (2006).
Subsp. powellii (syn.: A. hybridus subsp. hybridus var. pseudoretroflexus (Thell.) Carretero, A. hybridus subsp. powellii (S. Watson) Karlsson, A. chlorostachys Willd. var. pseudoretroflexus Thell.) (N-Am.) – A regular but poorly known alien, so far probably always ephemeral. Known at least since 1904 when it was found twice: in Schaarbeek and near Verviers. Early records were mostly confined to the valley of river Vesdre (probably as wool aliens). More recently also observed as a grain alien in numerous, widely spaced locations. Often seen on wasteland or by road verges and railway tracks. Remarkably frequently recorded on dumps, possibly as a birdseed alien.
Selected literature:
Aellen P. (1970) Amaranthus bouchonii Thellung en France. Monde Pl. 65: 367-368.
Bruynseels G. & Saintenoy-Simon J. (1983) Amaranthus bouchonii Thell., Herniaria hirsuta L. et Sorghum bicolor (L.) Moench dans la gare Josaphat (Schaerbeek, Bruxelles). Dumortiera 26: 27-29.
Costea M., Sanders A. & Waines G. (2001a) Preliminary results towards a revision of the Amaranthus hybridus species complex (Amaranthaceae). Sida 19(4): 931-974.
Dirkse G.M., Barendse R. & Abbink-Meijerink C.G. (1998) Amaranthus bouchonii Thell. (Franse amarant) en A. hybridus L. (Groene amarant) in Nederland. Gorteria 24: 69-80.
Duistermaat H. (1999) Nogmaals Amaranthus hybridus L. (Groene amarant) en A. bouchonii Thell. (Franse amarant). Gorteria 29: 31-33.
Duvigneaud J. & Lambinon J. (1976) Quelques Amaranthus intéressants ou nouveaux pour la flore belge. Dumortiera 2: 27-32.
Gaffney J. (1991) Amaranthus bouchonii in W. Norfolk. BSBI News 58: 42-43.
Iamonico D. (2012) Amaranthus powellii subsp. cacciatoi comb. et stat. nov. (Amaranthaceae). Nord. J. Bot. 30: 12-16.
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.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Amaranthus hybridus subsp. bouchonii. 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: 131.
Weaver S.E. & McWilliams E.L. (1980) The biology of Canadian weeds: 44. Amaranthus retroflexus L., A. powellii S. Wats. and A. hybridus L. Canad. J. Pl. Sci. 60: 1215-1234.
Wilkin P. (1992) The status of Amaranthus bouchonii Thellung within Amaranthus L. section Amaranthus: new evidence from studies of morphology and isozymes. Bot. J. Linn. Soc. 108: 253-267.
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.