Are traps of Utricularia multifida and U. westonii active and do they create negative pressure?

Utricularia multifida and U. westonii are Australian species classed recently with the subgenus Polypompholyx, which is comprised of the most evolutionary basal species. Their traps bear all functional structures necessary for negative pressure generation and suction ('firing'), i.e., active prey catching, but traps from tissue-culture-raised plants are not known to fire. However, presumably, plants in situ are active. Traps of terrestrial plants of both species raised from tissue culture were used for measurement of the critical negative pressure to further elucidate whether or not they could fire. According to our results, traps of U. multifida can be considered closed (i.e., no water flow between the trap inside and outside takes place) while those of U. westonii can be considered open. This study confirms great functional differences between the underwater traps in these species grown naturally (in an aquatic state) and those grown terrestrially in tissue culture.