The relationship among 80 different Echinochloa accessions were studied in 2000–2002 by applying amplified fragment length polymorphism (AFLP) analysis and examining the main morphological traits of these plants. The plants were collected from 40 different areas in which the main rice-growing region of northern Italy was divided on the basis of uniform environmental and agronomical conditions. Echinochloa accessions were grouped in three different species (E. crus-galli, E. erecta, E. phyllopogon) according to Pignatti's classification key and in four different species according to Carretero's taxonomy (E. crus-galli, E. hispidula, E. oryzicola, and E. oryzoides). The E. crus-galli accessions clustered as a specific group under both AFLP analysis and morphological traits analysis carried out according to Pignatti's and Carretero's keys. AFLP analysis revealed a separate group containing two accessions with a green basal stem section. These were classified as E. crus-galli by Pignatti's taxonomy and E. oryzoides according to Carretero's taxonomy. A red basal stem section, a trait not considered by either morphological classification, was the main morphological trait that characterizes all E. crus-galli accessions. All other accessions with green basal stem section clustered in a group that included E. erecta and E. phyllopogon according to Pignatti's taxonomy and E. hispidula and E. oryzicola according to Carretero's taxonomy. All species were evenly distributed in the monitored rice area, except the two E. oryzoides accessions, which were found only in the southwestern zone.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; junglerice, E. colonum (L.) Link ECHCO; late watergrass, E. phyllopogon (Stapf) Vasc. ECHPH; gulf cockspur, E. crus-pavonis (H. B. K.) Schultes ECHCV; early watergrass, E. oryzoides (Ard.) Fritsch. ECHOR; E. hostii (Bieb.) Boros; E. erecta (Pollacci) Pign.; E. hispidula (Retz.) Nees ex Royle; E. oryzicola (Vasing.) Vasing; rice, Oryza sativa L.