Trends of Specialization in Pollen of Flacourtiaceae with Comparative Observations of Cochlospermaceae and Bixaceae

Pollen from 17 genera of Flacourtiaceae was examined by SEM and TEM; twelve of them represented the primitive tribes Berberidopsideae and Oncobeae. Small, minutely structured grains are widespread in this family, and have often been lumped together as one morphological type. A study of the relative thickness of the tectal layers, and of the ar-rangement and size of columellae and perforations indicates that not all minutely structured grains are homologous in development. Most genera of Berberidopsideae and Oncobeae can be termed microperforate tectate, as the muri are x2-5 as wide as the lumina and both features are less than one micrometer in diameter. Berberidopsis pollen is unique in the Flacourtiaceae in being tricolpate and in having a rough, thick tectum infrequently traversed by microperforations 0.03 p. in diameter. Tendencies toward perreticulate structure occur in Mocquerysia. Development of a high infratectal space is illustrated by Casearia nitida and an intectate exine in the related Samyda dodecandra. Pollen of Cochlospermum and Bixa are distinct from Flacourtiaceae and show independent trends of specialization.