Amaranthus palmeri S.Watson, Proc. Amer. Acad. Arts, 12: 274. 1877.

© 2015 Filip Verloove, Nicola M. G. Ardenghi

( Amaranthaceae)

Naturalized neophyte new to the flora of Piemonte (Conti et al., 2005; Celesti-Grapow et al., 2009a; Iamonico et al., 2015; Iamonico, 2015).

Received: 10 th January 2015

Accepted for publication: 19 th April 2015

ITALY. Piemonte. Prov. Alessandria: Tortona, river Scrivia at railway bridge, gravelly riverbed, locally, along with A. tuberculatus, 09.09.2014, F. Verloove 11206 (BR) .

A native of the southwestern U.S.A. and Mexico, Amaranthus palmeri now occurs as a weed in Europe, Asia and Australia (Mosyakin & Robertson, 2003). In Italy it was recently discovered in Emilia-Romagna, in the province of Ravenna (Iamonico et al. 2015; Iamonico, 2015). While for many decades it remained strictly casual in Europe (often associated with imported cereals or soybeans; e.g. Verloove & Vandenberghe, 1993), it managed to naturalize locally in recent times, especially in the Mediterranean area. In Spain naturalized populations were detected around Lleida in 2007 (Verloove & Sánchez Gullón, 2008) and soon afterwards it proved to have become a troublesome agricultural weed in maize fields there (Recasens et al., 2013). Elsewhere in the Mediterranean area stable populations are known from Israel and Greece (Raus & Raabe, 2006). In Ravenna province the plant was regarded as casual (Iamonico et al., 2015; Iamonico, 2015), even though the species was confirmed for at least two years consecutively in the same site (see http://www.actaplantarum.org/floraitaliae/viewtopic.php?f=106&t=67866, retrieved on December 2014); in Tortona the population is clearly naturalized.

Amaranthus palmeri is a dioecious species. In Italy a related species, A. tuberculatus (Moq.) J.D.Sauer, has been known since 1975 (Soldano, 1982). It now has become an invasive species in riparian habitats and cultivated fields (Banfi & Galasso, 2010), especially in the plain of river Po and its tributaries. Since A. palmeri is equally aggressive and occurs in the same type of habitats, similar behavior is predictable. Both species are rather alike and may have been confused. A. palmeri has much longer bracts and tepals, the inflorescence therefore being stiff and prickly in appearance. In Tortona, along Scrivia river, both grow sympatrically.