Tetrad arrangement of the trisaccate pollen of Dacrycarpus dacrydioides (Podocarpaceae) and developmental morphology of the triradiate ridge

Abstract

In Dacrycarpus dacrydioides (Rich.) De Laubenfels (Podocarpus d.) study of the arrangement of the microspores at the tetrad stage reveals that the two pairs of sister-microspores cross at an angle of about 90°, and each microspore has one apex of its triangular aperture orientated towards the sister-microspore and the other two apices face the opposite direction. Consequently, the twelve aperture apices of the tetrad meet two and two at six points. At the first stage of development the rugulate processes on the proximal face observed in SEM are very marked, and the arms of the triradiate ridge are pronounced and sinuous; at the further stages, however, the sexine of the central part becomes more or less smooth, and the arms of the triradiate ridge become straight and less visible, or disappear. A hypothesis is proposed to tentatively explain this unusual sculptural development.