Pollen morphological differences in Amaranthus species and interspecific hybrids

This study examined pollen morphological variation among Amaranthus species and interspecific hybrids. Ten weedy Amaranthus species, a cultivated grain species, and several putative hybrids resulting from interspecific mating between common waterhemp and Palmer amaranth were grown in a greenhouse. Mature pollen was collected, viewed, and photographed with a scanning electron microscope (SEM). The pollen grains were spherical shaped with polypantoporate, or golf ball-like, aperture arrangement. Differences were observed between the monoecious and dioecious Amaranthus species. Pollen grains of the dioecious species had a greater number of apertures on the visible surface. One exception to these trends was the dioecious species, Palmer amaranth, whose pollen was similar to that of the monoecious species spiny amaranth. However, pollen grain diameters did not differ between the monoecious and dioecious plants. Significant differences also were noted between the pollen from the putative common waterhemp ×× Palmer amaranth hybrids and the parental-type pollen grains. Pollen of the hybrids was similar in size to the maternal parent but had an aperture number that was intermediate between parents. This indicates that pollen characteristics may be controlled by the female and that hybrids may be more prevalent than originally thought.Nomenclature: Common waterhemp, Amaranthus rudis Sauer AMATA; grain amaranth, Amaranthus cruentus L. AMACR; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; Powell amaranth, Amaranthus powellii S. Wats. AMAPO; prostrate pigweed, Amaranthus blitoides S. Wats. AMABL; redroot pigweed, Amaranthus retroflexus L. AMARE; sandhills amaranth, Amaranthus arenicola I. M. Johnst. AMAAR; smooth pigweed, Amaranthus hybridus L. AMACH; spiny amaranth, Amaranthus spinosus L. AMASP; tall waterhemp, Amaranthus tuberculatus (Moq.) J. D. Sauer AMATU; tumble pigweed, Amaranthus albus L. AMAAL.