Comparison of riverside herb communities with weed vegetation in the tropical lowlands of Peru.
Plant communities were compared in the lower course of the Yuyapichis river including agricultural areas and open places around houses, and alongside other river types. River bank communities had a fairly characteristic species composition of mostly neotropic distribution. The group of plants restricted to agricultural areas was only weakly developed but included the 2 important weeds Chamaesyce hirta and Rottboellia exaltata. This group, as well as species occurring in both areas, had a mostly pantropic distribution reaching into the Holarctic region, such as Eleusine indica, Portulaca oleracea and Cynodon dactylon. Species patterns along the river banks were determined by different flooding characteristics. Changes in species composition were particularly marked at river estuaries. Photographs from the river Pachitea showed a high proportion of therophytes with pantropic distribution as far as the Holarctic region, whereas most of the species of the upper reaches of the Yuyapichis had a neotropic distribution.