Pollen morphology of the Orobanchaceae and rhinanthoid Scrophulariaceae

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Abstract
The Scrophulariaceae is a large family of primarily herbaceous plants, containing some members which are root parasites, while others are non-parasitic. The parasites are all within the subfamily Rhinanthoideae, while most of the nonparasites have been included in the Antirrhinoideae. The Orobanchaceae is a small family, all of whose members are root parasites. The two families are generally considered closely related, so much so, that several genera (Buchnera, Harveya, Hyobanche, and Lathraea) have been moved back and forth between the families. In this study, light microscopy, scanning electron microscopy, and transmission electron microscopy were used to examine the pollen of 57 taxa: members of the Orobanchaceae and Rhinanthoideae, and several members of the Antirrhinoideae for out group comparisons. The resulting data showed no clear differences between the pollen of the Orobanchaceae and that of the rhinanthoid Scrophulariaceae. The grains were typically isopolar, radially symmetrical, more or less spheroidal, and tricolpate. The most common exine surface sculpturing was retipilate. The antirrhinoid pollen had two major differences: The apertures were tricolporate and the predominant exine surface was reticulate. The pollen of the Rhinanthoideae is closer in form to that of the Orobanchaceae, than it is to the pollen of the Antirrhinoideae. Digitalis, a non-parasitic member of the Rhinanthoideae, had pollen very similar to that of the members of the Antirrhinoideae.