Abstract
Summary: The plants of Podostemaceae, an unusual aquatic angiosperm famiy that occur in rapids andwaterfalls, gained a horizontal axis ofdevelopment at the beginning of the famiy, whie lost the verticalbipolar development common in angiosperms. The gain and loss of the axes took place in the seedling stage: the secondary root develops from the hypocotyl or the secondary shoot develops from the axil of the cotyledons. The primule and radicle on either end of the hypocotyl became reduced or disappeared. The crustose rootunique to Podostemoideae evolved with the loss of the root apical meristem and the development of themariginal meristem.
