Pollen Ultrastructure of the Philydraceae

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Abstract
Pollen morphology, sculpturing, and wall ultrastructure of the five species in the monocot family Philydraceae were investigated in order to assess phylogenetic relationships. All members of the Philydraceae have monosulcate, heteropolar pollen grains with a tectatecolumellate exine having distinctive lamellae inner to the foot-layer. Histochemical tests of Philydrum lanuginosum indicate an ektexinous exine composition. The aperture wall of all members of the family consists of a thick, 2-layered intine with exine absent or composed of scattered deposits. The inner intine layer is infused with numerous vesicular or channellike structures. Histochemical tests of Philydrum lanuginosum suggest that the outer intine layer is primarily cellulosic and the inner intine layer is pectic-rich, a trend opposite from that noted in pollen of other monocot taxa. Palynological similarities between the Philydraceae and related families, including monosulcate apertures and a tectate-columellate exine, are hypothesized to represent ancestral features which are of no value in assessing phylogenetic relationships.