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.