A few representatives of the monocot broadleaf weed genus
Heteranthera such as Heteranthera reniformis are presumably of
American origin (http://www.hear.org/pier/species/heteranthera_
reniformis.htm, visited February 9, 2015). Today, they are rather
typical of European rice fields. They can, however, also cause
problems in some Brazilian and US American rice fields. Sagittaria
species are also well adapted to aquatic and wetland conditions.
There are, however, preferences of single species. Sagittaria montevidensis
Cham. & Schltdl. is reported as typical of Australian, US
American, and Brazilian rice fields whereas Sagittaria trifolia L.
seems to be more frequent in Asian countries such as Japan, Korea,
and Vietnam. In Europe, Sagittaria species are no major problem
weeds in rice. This is also true for Monochoria species. Several
aquatic dicots which found their way into rice fields are sometimes
referred to as complexes as there are often several species involved.
One example is the “Ludwigia-complex”. In Brazil, this consists
primarily of Ludwigia elegans (Cambess.) H. Hara, Ludwigia longifolia
(DC.) H. Hara, and L. octovalvis (Andres et al., 2013b). In Asia, we find
L. octovalis and other Ludwigia species (Table 8). Lindernia procumbens
(Krock.) Philcox syn Lindernia pyxidaria L. is a species of
Eurasian origin which is a rather rare wetland pioneer in northern
Europe. It is, however, more frequent in warmer climates of the
northern hemisphere. Climate creates preferred niches. However,
the background for regional preferences in aquatic species is in
many cases not clear yet.