Resumo. The objectives this study were to: (a) quantify the seasonality evapotranspiration of understory vegetation (ET rasteira), (b) quantify the influence of ET rasteira on total evapotranspiration (total ET) and (c) verify the relation between ET rasteira and Leaf Area Index of the understory vegetation (LAI rasteira), open canopy and soil water potential, in four distinct landscapes: Cerrado stricu sensu, Gallery Forest, Brachiaria pasture and Eucalyptus reforestation, situated in the APA Gama-Cabeça de Veado, Districto Federal. An open-top chambers for understory vegetation, non-dispersive infrared gas analyzer, plant canopy and leaf area index analyzer; and soil psychrometers were used to collect data. The ET rasteira contributed significantly to total ET, mainly during rainy season, approximately 60 % of the annual mean of total ET, in Cerrado strictu sensu and Gallery Forest areas. Significant and directly proportional relationships between ET rasteira and the understory LAI, open canopy and soil water potential were observed, this influenced by rain seasonality.