COMPARATIVE POLLEN MORPHOLOGY OF 5 NEW-WORLD GENERA OF PODOSTEMACEAE

The Podostemaceae are the largest family of strictly aquatic angiosper ms; however, relatively little is known about the palynology of the fa mily. Pollen micromorphology and ultrastructure of five representative New World taxa are described, including Marathrum rubrum Novelo & Phi lbrick, Oserya coulteriana Tul., Podostemum ceratophyllum Michx., Tris ticha trifaria (Bory ex Willd.) Sprengel, and Vanroyenella plumosa Nov elo & Philbrick. Pollen grains from all five species are relatively sm all spherical, microechinate, have a tectate-granular sexine and a thi ck nexine in non-apertural regions, and a semitectate sexine and a thi n nexine in apertural regions. Characters that vary among the taxa inc lude dispersal unit (monads or dyads), sculptural element morphology, infratectal granule size, and aperture morphology and ultrastructure. This is the first study to describe the pollen morphology of these fiv e taxa in detail, and it is the first to illustrate the ultrastructure of pollen wall characters for any member of the family. (C) 1997 Else vier Science B.V.