The study of the floristic composition of weeds of an area or agricultural region is important since it identifies the diversity of species and provides management strategies to be used under various agricultural system conditions. The objective of this work was to identify the floristic composition of weeds occurring in guaraná crops in five counties (Coari, Iranduba, Maués, Presidente Figueiredo and Urucará) located in the state of Amazonas, Brazil. Samples of weeds were taken from guarana growing areas in the five counties and identified by class, family and species. A total of 14,707 individual plants were collected and grouped into 40 families and 87 species,as follows: 70 Dicotyledonous, 13 Monocotyledonous and 4 Pteridophyts. The Dicotyledonous class presented the largest number of families and the monocotyledonous the largest number of individual plants, except in Maués and Iranduba. The number of Pteridophyts was inexpressive in all the counties. The Poaceae and Asteraceae families presented the largest number of species. Poaceae was found in all the counties, presenting the largest number of species in Maues. Panicum pilosum was the species with the largest number of individual plants, frequency, density and value of importance index, while Panicum laxum presented an expressive number of species in Urucará and Iranduba. Scleria malaleuca presented an expressive number in Coari and Chamaesyce hirta in Maués. Homolepis aturensis, Paspalum conjugatum and Spermacoce capitata were found in the five counties. The largest species diversity was found in Maues whereas the largest number of individual plants was found in Coari. The largest similarity index was found between Iranduba and Presidente Figueiredo (45%) and the smallest between Iranduba and Coari (21.43%).
guarana crop; phyto-sociology; weeds; frequency; Amazonian
