XVI International Botanical Congess

Field observations were made at Parque Nacional Iguazú (Misiones, Argentina) on January 1998. The plants grew in a low grassland. Flowers opened at 5.30 am (at 5.45 am there was full light) and were closed by 7 p.m. Three floral phases were identified: the first and the third, donors of pollen, the second, donor and receptor. Sometimes flowers ended anthesis in phase 3, without closing, except when it rained. Total percentage of sugars in nectar was 29 ± 5 (n=12), it was not diluted by rain. The greater volume was secreted during phase 2, phase 3 did not produce nectar. The predominant color in the visible spectrum is yellow green with purple. Slight odor, similar to citronella or cinnamon, somewhat citric, is present in all floral phases, stronger in the second one. It is perceived in the radii. Stigmas were receptive the whole anthesis. The function of each visitor species was established: Ptiloglossa sp. (Hymenoptera, Colletidae), pollinator, Heleomyzidae (Diptera), nectar thief, Chrysomelidae (Coleoptera) and Ensifera (Orthoptera), pollen robbers and florivores. A compatible experiment carried out suggests P. misera is self-incompatible (19% fruits from free pollination vs. 0% from spontaneous self-pollination).