Abstract By means of hand pollination experiments and fluorescence microscopy the breeding systems and pollen tube growth were studied in Dolichandra cynanchoides and Tabebuia nodosa , two bignoniaceous species of the Chaco woodland of NE Argentina. Both species abscised all selfed pistils within 4–8 d although self pollen tubes grew successfully to the ovary and penetrated many ovules. Both species therefore show ‘late-acting self-incompatibility’ (LSI) or ‘ovarian sterility’ (OS) type control of selfing. LSI-OS has been reported in 17 species of the Bignoniaceae, and is also clustered in families such as the Bombacaceae-Sterculiaceae, Fabaceae and Myrtaceae. The implications of such family clustering are discussed, with regard to current hypotheses for the action of LSI-OS phenomena.