XVI International Botanical Congess

Field observations were made at Quebrada del Toro (Santa, Argentina) from March until May, 1995. The population studied exhibited chasmogamous and cleistogamous flowers. The first ones offered nectar (very little), anthesis lasted 12 hours and they did not receive visitors. The others were defined in that way because they had half the size of the chasmogamous ones and performed an outline of anthesis (only the left wing displayed and before 30 minutes folded over itself). Pollen, scarce but highly viable, was already on the stigmas at the bud stage. Both type of flowers produced fruits, so this species is self-compatible. The high frequency of cleistogamous flowers in this riparian environment, in contrast with the presence of only chasmogamous ones in mountain grasslands, suggested us the following hypothesis: the production of the flower types varies according to the place the plants grow in.