Amaranthus L. (Amaranthaceae) is a
genus consisting of about 70 species, about
40 of which are native to America, while
the remaining ones are native to the other
continents (Costea et al. 2001). Most of the
species recorded in Europe are considered
alien species causing social (allergenic plants),
economical (crop weeds) and ecological
impacts (loss of biodiversity). Moreover,
the whole genus is considered critical as for
taxonomy and nomenclature, and for the
frequent misapplication of names.
The Amaranthus hybridus group includes
six closely related species (sensu Costea et
al. 2001) that are considered the most critical
ones both for taxonomy and for morphological
variability. Consequently, the identification of
the species within this group is very difficult.
In this paper, A. powellii S. Watson subsp.
powellii is recorded for Lazio region (central
Italy) for the first time. The morphology of
the species, its distribution, its invasive status,
ecological features for Italy and taxonomical
notes are also treated. Moreover, a comparison
with the related subspecies A. powellii S.
Watson subsp. bouchonii (Thell.) Costea &
Carretero is provided.