This work aimed to obtain equations to estimate the leaf area of weed species of the Amaranthus genus, using leaf blade linear dimensions, as well as to compare the equations set up for plants grown under greenhouse and field conditions. Thus, plants of A. deflexus, A. hybridus, A. retroflexus, A. spinosus and A. viridis were grown in the greenhouse or collected in natural infestations of agricultural or non-agricultural areas of Piracicaba-SP, Brazil. For each condition, maximum length (C) and width (L) dimensions, as well as real leaf area (Ar) per leaf were measured in 100 leaf blades. The data groups were adjusted to linear equation crossing the origin Ar = a.(C.L) and compared through confidence intervals of 5% significance for all variables. It was concluded that: weed species of the Amaranthus genus display differential leaf sizes, with A. deflexus presenting the smallest dimensions, on average; the linear equation crossing the origin (Ar = a.(C.L)) was adequate to adjust the relation between linear blade dimensions and real leaf area; plants grown under greenhouse and field conditions may present differences in leaf size or in the a parameter of the adjusted equation.
pigweed; leaves; growth; linear adjustment
