Bacopa llanorum, a new species from the seasonally flooded savannas of the “Llanos” region of Colombia (Arauca department) is described and illustrated, and its morphological relationships are discussed. On the basis of its dimorphic leaves (the innermost blade filiform, uppermost lanceolate-ovate), the new species does not appear to be allied to any other Bacopa species. However, it shares several other features with B. reptans. A new combination, Bacopa debilis, is proposed to replace Caconapea debilis. In addition, ecological information of the genus in “Los Llanos” of Colombia and Venezuela, and ecological and floristic notes about the eolic-limose plains, are included. A key for identifying species of Bacopa in this region is also provided. Bacopa llanorum is remarkable for its foliar dimorphism, in an otherwise predominantly homomorphic-leaved genus, and it increases to 20 the number of species of the genus in the “Llanos del Orinoco” bioregion.