Pollen Morphology of Tribulaceae

The pollen morphology of the Tribulaceae Hadidi, was investigated by means of LM, SEM, and TEM. In the Tribulaceae, two completely different pollen types are encountered, each restricted to one of the two stenopalynous subfamilies. The Tribuloideae invariably have polypantoporate, spheroidal, sometimes slightly elliptical, reticulate pollen grains, in which each lumen contains a pore. In the Neoluederitzioideae the pollen grains are 3-colpate or 3-colporate, isopolar, radially symmetrical and the exine structure consists of a perforate tectum supported by infratectal bacula. The pollen morphology strongly supports the segregation of the separate family Tribulaceae from the Zygophyllaceae (El Hadidi 1977), and its subdivision into two subfamilies the Tribuloideae and the Neoluederitzioideae. Since the Tribuloideae are clearly stenopalynous and include ca. 60 species, the pollen morphology, with a few exceptions, does not seem to be very useful at the generic and specific level. Both tribes of the Neoluederitzioideae are distinct due to the difference in the size of pollen grains and their apertural condition.